- Email: [email protected]
Applications of ultrasound in dentistry
Ultrasound in Med. & Biol Vol. 14, No. l, pp. 7-14, 1988 Printed in the U.S.A.
0301-5629/88 $3.00 + .00 © 1987 Pergamon Journals Ltd.
OOriginal Contribution APPLICATIONS
OF ULTRASOUND
IN DENTISTRY
A. D. W A L M S L E Y Department of Dental Prosthetics, The Dental School, St. Chad's Queensway, Birmingham, B4 6NN (Received 11 February 1987; in revisedforrn 29 May 1987) Abstract--An ultrasonic descaler working at kHz frequencies is used in dentistry to remove attached deposits from the teeth. Such devices offer many advantages over conventional hand instruments by reducing both the work and time involved in the clinical descaling process. Although it is a recognised clinical instrument, there has been little attempt to standardise its acoustic power output. A parameter which may characterise adequately the acoustic emission from these instruments is the displacement amplitude of the probe tip. Modification of the ultrasonic descaler generator has led to the further use of the instrument in other dental areas. Diagnostic applications of M H z ultrasound is limited by the structure and arrangement of the dental tissues. Therapeutic ultrasound has been used to treat a variety of dentally related ailments, and ultrasonic cleaning baths are used to clean both dental instruments and materials.
Key Words: Ultrasound, Dentistry, Clinical applications.
INTRODUCTION The common perception of the use of ultrasound from a medical point of view is in its wide use in areas such as diagnostic imaging and physiotherapy. Within the wider aspects of medicine however ultrasound finds considerable uses in the practice of dentistry. One of the earliest references to its use in the dental sphere was in 1952, where an industrial ultrasonic impact grinder was used to prepare cavities in extracted h u m a n teeth (Balamuth, 1963). This quickly caught the imagination of dentists and the potential use of such an ultrasonic dental drill was reported by Catuna (1953), with aa instrument being introduced eventually for cavity preparation in the teeth of patients (Nielsen and Richards, 1954; Roche, 1954; Oman and Applebaum, 1955). These early instruments operated at a frequency of around 29 kHz using an abrasive slurry ofaluminium oxide particles to assist in the cutting process. Tooth substance was removed efficiently by this technique (Postle, 1958). There was little patient discomfort and it was suggested that cavity preparation could be performed without recourse to local anaesthesia. Furthermore, as a low contact load was employed in cutting, potential traumatic effects on the underlying vascular and nervous tissues of the dental pulp were reduced. However, ultrasonic cavity preparation never became popular due to poor visual access and the large
amount of aluminium slurry used during cutting which required removal. As a result it was superseded by the more effective high speed rotary drills (Street, 1959) which were developed around the same time. The role of ultrasonics in dentistry did not disappear altogether since previously Zinner (1955) had adapted the original ultrasonic drill for use in the removal of dental plaque and calculus from the surface of the teeth (descaling). This process was first demonstrated clinically by Johnson and Wilson (1957) and is now a widely accepted clinical procedure. By the seventies it was reported that within the United States of America there were some 50,000 to 100,000 ultrasonic devices in use for descaling and periodontal treatment (Lees, 1972; Frost, 1977). At the present time the number of units is likely to be far in excess of this number worldwide although accurate figures do not exist. The use of ultrasound in dentistry is not restricted to the descaling of teeth, however, and its application in other areas has been steadily increasing (Balamuth, 1967). The ultrasonic descaler has been modified for use also in root canal therapy (endodontics), amalgam packing, extraction of teeth, and displacing cemented restorations from teeth. Other applications of ultrasound in dentistry include the treatment of joint and muscle related ailments around the face, the generalised cleaning of both instruments prior to sterilisation and dentures, and as a
8
Ultrasound in Medicineand Biology
Volume14, Number 1, 1988
diagnostic procedure to detect dental caries and periodontal disease. ULTRASONIC DESCALING The supporting tissues of the natural human tooth (Fig. 1) consist of the gingivae, the periodontal ligament, and the alveolar bone, collectively termed the periodontium. These tissues may be subject to inflammatory change which, if left untreated may lead to irreversible damage with subsequent loss of the teeth. The primary etiological factor in periodontal disease is the deposition and accumulation of dental plaque on the surfaces of teeth (Lre et at., 1965). Dental plaque is a soft tenacious bacterial deposit which forms on the surface of a tooth when oral hygiene methods are ineffective or abandoned (McHugh, 1970), and the control of plaque formation and its effective removal is an essential requiremetn for periodontal health (Lre, 1970). If dental plaque is allowed to accumulate, deposition of calcium salts in its matrix will result in the formation of dental calculus, which consists mainly of 80% inorganic matter mainly in the form of calcium phosphate as hydroxyapatite, and inorganic matter comprising mainly desquamated epithelial cells and bacteria (Jenkins, 1966). Calculus acts as tissue irritant by virtue of its roughness, bacterial content, and by the accumulation of further dental plaque deposits on its surface (Allen and Kerr, 1965; Schroeder, 1969). The main application of ultrasound in dentistry therefore is to remove both dental plaque and cal-
~
Gn i gvia P i de onnttal Lg iearo m
~
Enamel
I~
Pupl Denn tie
Root
Cemenu tm A v l e o a l Bone r Fig. 1. A schematic diagram of the constituents of the tooth and its supporting tissue.
Fig. 2. The ultrasonic descaler being used clinically to remove attached deposits from the surfaces of the teeth.
culus deposits from the surfaces of teeth (Fig. 2) using an ultrasonic descaler (Suppipat, 1974). These instruments operate at frequencies of 25-42 kHz and are useful in that they reduce the mechanical effort required by the clinician. Furthermore they are easy to operate and there is a reduction in both the treatment time and the level of discomfort to the patient. These devices utilise a rigid metal probe which is driven to oscillate in its longitudinal mode. It is this vibratory motion that provides the "chipping" action which removes the attached deposits from the teeth. A magnetostrictive or a piezoelectric transducer within the handpiece is used to produce the ultrasonic vibrations. In magnetostrictive designs, the metal probe is attached to a laminated ferromagnetic stack (Fig. 3a). Each probe has its own integral stack being known as an "insert" and this is powered by the same generator via coils in the handpiece. Piezoelectric devices are much simpler in design in that the different probes are interchangeable with the one transducer. Both designs utilise a flow of cooling water which is passed through the handpiece and onto the oscillating tip. The cooling water serves to reduce frictional heating at the tooth/tip interface and in magnetostrictive transducers it also is used to cool the ferromagnetic stack. On reaching the tip, cavitational activity occurs within the water (Walmsley et al., 1986a), and thus may also contribute to the removal of the attached deposits (Balamuth 1967; Walmsley et al., 1984). A variety of probe tip designs are used in the descaling process and examples of the more commonly used probes are shown in Fig. 3b. They range from straight or sickle probe tips approximately 2-3 cm long and 0.2 cm broad at the tip to angled/blade designs incorporating a 0.5 by 1 cm blade tip. Such designs are used for different clinical tasks such as
Applications of ultrasound in dentistry • A. D. WALMSLEY
(a)
(b)
Fig. 3(a). An example of inserts for a magnetostrictive generator are shown; (b) Three commonly used designs of descaling probe tips: A, straight; B, angled blade, and C, sickle. general descaling and root planing (which will be discussed below). They are all based on conventional hand-held instrument designs as it is assumed by both manufacturers and clinicians that both forms of descaling achieve the same result. During oscillation, clinicians anticipate that the oscillatory movement of the descaling tip will occur along the longitudinal axis of the instrument (Johnson & Wilson, 1957). The direction of oscillation observed, however invariably occurs at an angle O to the longitudinal axis of the instrument (Fig. 4). This angle is approximately 5 ° for the straight probe designs and 30 ° for sickle/angled designs (Walmsley el al., 1986b). Although most designs exhibit a true longitudinal motion, some of the more complex probe tips demonstrate an open elliptical motion. Comparison to conventional instrumentation Although ultrasonic descaling is effective in the removal of dental plaque and calculus, the use of
9
hand instruments may also achieve similar clinical results. Therefore the majority of clinical investigations in relation to the ultrasonic descaler have been concerned with its efficiency when compared to manual methods and to assess which, if any, is superior. Clinical studies on the quality of the descaling process show that both manual and ultrasonic instrumentation remove the attached calculus from the tooth surface efficiently with no apparent differences between either technique (McCall and Szmyd, 1960; Stende and Schaffer, 1961; Moskow and Bressman, 1964). These initial findings were followed by scanning electron microscope studies of the enamel and dentinal surfaces following routine descaling procedures. This suggested that ultrasonic devices tended to remove the calculus in small fragments with burnishing of the remaining deposits, whilst hand instruments removed the calculus in much larger fragments (Jones et al., 1972). However, calculus removal by the ultrasonic descaler was superior from those teeth where there was good access. In patients suffering from periodontal disease there is often a surface layer of necrotic cementum overlying the root. This necrotic cementum contains bacterial products which may be irritant to the periodontal tissues (Hatfield and Baumhammers, 1971; Aleo et al.. 1974) and the removal of this surface layer of cementum (root planing) is an established part of the descaling process (Rosenberg and Ash, 1974; Robinson, 1975). After a course of descaling and root planing, Torfason et al. (1979) showed that both hand and ultrasonic instrumentation produced similar rates of resolution of inflamed periodontal tissues. However, this result has been disputed by Nishimine and O'Leary (1979) who reported that, in root planing, hand instruments were superior to ultrasonic descalers. A generalised conclusion from the above studies is that for either root planing or areas of the mouth where access is difficult, ultrasonic descalers are relatively ineffective (Stende and Schaffer, 1961; Suppipat, 1974; Nishimine and O'Leary, 1979) and a further course of descaling with hand instruments is usually required to achieve a clinically satisfactory
Longitudinal Axis
Fig. 4. A diagrammatic representation of the probe oscillations which occur at an angle (O) to the longitudinal axis of the instrument.
10
Ultrasound in Medicineand Biology
result. This is generally related to both the lack of operator tactile sensitivity when utilising the instrument and poor visibility created by the associated aerosol spray. The efficiency of any descaling technique may also be assessed by the eventual healing and resolution of the periodontal tissues. In clinical studies, most investigators agree that tissues surrounding teeth that are subjected to ultrasonic descaling show more rapid resolution to health, as demonstrated by a larger reduction in the tissue inflammation, than where a hand instrument was used (Goldman, 1961 ; Schaffer et al., 1964; Sanderson, 1966; Walsh and Waite, 1978). This may be due to an increased rate of collagen production stimulated by the ultrasonic descaler (Bhasker et al., 1972). However, at these frequencies the effect of the ultrasound may chiefly be hormetic (Williams, 1983), that is, a beneficial or stimulating effect resulting from the application of a small "dose" of a harmful or irritating agent. Generally, most investigators cite the presence of a water spray, with its lavage action irrigating the tissues, as the major reason for the superiority of the ultrasonic descaler (Clark, 1969; Bhasker, et al., 1972; D'Silva et al., 1979). However, no consideration was given in any of the above reports to the role of cavitational activity within that water supply and its potential cleaning action. Clinical evaluation
The main advantage claimed for the use of an ultrasonic descaler is that calculus removal is accomplished more rapidly than with conventional hand instruments (Johnson and Wilson, 1957; Torafason et al., 1979) and time savings of 20% (Forrest, 1967) to 50% (Donz~ et al., 1973) have also been reported. However, it appears that for efficient removal of calculus, the same amount of time is involved regardless of the technique used (Burman et al., 1958), although ultrasonic descaling may be quicker for mandibular teeth (Stewart et al., 1967). During clinical treatment the majority of patients appear to prefer ultrasonic descaling to hand instrumentation (Johnson and Wilson, 1957; Forrest, 1967; Donz6 et al., 1973) and this may be attributed to a reduction in discomfort (Johnson and Wilson, 1957). Clearly this is an advantage in situations where the tissues may be unduly susceptible to pain in the presence of infection (Wilson, 1958). In addition, many clinicians prefer using the ultrasonic descaler (Stewart et al., 1967) which may be related to a reduction in both physical effort and complex manipulation. However, the possible loss of tactile sensation when using the device makes it diffi-
Volume14, Number 1, 1988 cult to be sure that all calculus has been removed completely, a problem that does not appear to exist when using hand instruments (Burman et al., 1958; Moskow and Bressman, 1964; Schaffer, 1967). I n s t r u m e n t standardisation
Many investigations into the performance of the ultrasonic descaler, may be criticised due to the fact that there was inadequate standardisation of the operating instrument. The clinical settings of the working ultrasonic descaler have ranged from the use of either "medium" or "high" power levels used in conjunction with a free flow of water (Moskow and Bressman, 1964; Jones et al., 1972; D'Silva et al., 1979) to a power setting and flow of cooling water adjusted to the "operator's preference" with the precise conditions not being reported (Sanderson, 1966; Torfason et al., 1979). Some investigators gave no details of the working conditions of their instrument (McCall and Szmyd, 1960; Goldman, 1961; Stende and Schaffer, 1961; Donz~ et al., 1973). Other variables which are not adequately described are the time spent and the application loads used during operation. Interpretation and comparison of the results obtained from different workers is difficult, therefore, due to these discrepancies in the instrument standardisation. Although there are various methods used to measure the acoustic power output emitted from medical transducers operating at MHz frequencies (Wells, 1977), there is no commonly agreed technique used for representing the power output from ultrasonic descalers working in the kHz range. The majority of these instruments are designed with a control dial enabling the operator to vary the amount of electrical power input to the transducer, and an estimate of this is displayed on an arbitrary linear scale. This scale, however does not provide a meaningful estimate of any relevant acoustic emission from the probe tip. A parameter which adequately characterises the acoustic emission is the displacement amplitude of the oscillating tip (Walmsley et al., 1986a). The displacement amplitude may be measured using a travelling light microscope at an overall magnification of 100×. This provides a direct measure of the "chipping" action of the probe tip when used clinically. Displacement amplitudes for the descaling tips range from 18-27 gm for straight probes and from 27-65 um for sickle probes (Walmsley et al., 1986b). It has been shown that differing designs of the descaling tip exhibit different displacement amplitudes at the same nominal power output from the same generator. Furthermore, different generators from the
Applications of ultrasound in dentistry • A. D. WALMSLFY
same manufacturer produce a different range of displacement amplitudes when the same probe design is used (Walmsley et al., 1986b). The displacement amplitude not only gives a measure of the amount of"chipping" action but also gives a direct measure of cavitational activity occurring within the associated cooling water (Walmsley et al., 1986a). When measured by chemical dosimetry methods, an apparent "threshold" for the onset of cavitational activity occurs at displacement amplitude of 12 um. It is then found to increase in a linear manner with increasing displacement amplitude of the probe (Walmsley et al., 1986a). A measure &electrical power input to the transducer is meaningless (using the manufacturers control dial) because the transduction process is inefficient. This is demonstrated by a nonlinear increase in the displacement amplitude with increasing power setting (Walmsley et al., 1986a; 1986b). As the displacement amplitude appears to be a satisfactory method of determining the efficiency of an ultrasonic descaling tip, measurements for the individual probes in relation to acoustic power output should be displayed in manufacturers literature. This is necessary in order to regularize and improve clinical performance and allow meaningful comparison of results between different clinical investigators.
11
file (Fig. 5). This oscillating file is placed within the root canal of the tooth and abrades the walls removing contaminated organic and inorganic material. An antiseptic solution (usually sodium hypochlorite) is often passed over the oscillating tip to aid in the cleaning process (Cunningham et al., 1982; Griffiths and Stock, 1986). The occurrence of acoustic microstreaming fields developed around small irregularities protruding from the file surface increases the effectiveness of the disinfectant (Ahmad et al., 1987). Cavitational activity has been shown not to occur along the oscillating file and this is probably related to the relatively low displacement amplitudes produced when it is oscillating within the canal (Ahmad et al., 1987). These instruments have been subject to investi-
(a) L
T
MODIFICATIONS OF THE ULTRASONIC DESCALER Apart from the routine descaling procedures, the basic principles of the ultrasonic descaler have found use in other areas of dentistry. Generally the generator remains unchanged but different shaped inserts are used to perform the particular clinical task that is required. Endodontics Ultrasonic vibrations may be used to prepare and clean the root canal of nonvital teeth before filling is commenced (Richman, 1957; Martin, 1976; Nehammer and Stock, 1985). The development of such instruments was pioneered by Martin in the early 1970s (Martin, 1976) and is now a well recognised and documented technique which is rapidly growing in popularity. These instruments are essentially a direct adaptation of the ultrasonic descaler where a rigid metal rod is driven to oscillate in its longitudinal mode. However, unlike the descaling instruments, a small file is attached near the end of the main driver and is set at an angle of 60-90 ° to the main longitudinal axis. Accordingly, during operation a transverse wave is set up along the length of the
Fig. 5(a). A diagrammatic representation of the ultrasonic endodontic instrument showing the main longitudinal oscillation (L) occurring along the main axis. The metal file is at right angles to the main instrument and a transverse oscillation (T) is set up along its length; (b) The transverse oscillation of the metal file consists of nodes (N) and antinodes (A). The tip of the file being unconstrained exhibits a large oscillation (from Walmsley, 1987).
12
Ultrasound in Medicineand Biology
gations which are mainly related to the clinical efficiency of the instrument. The advantages claimed for such treatment over conventional methods include cleaner root canals with increased debris removal and a reduction in bacterial contamination (Martin et al., 1980; Cunningham et al., 1982). The majority of investigators have not adequately standardised their instruments, making comparison between different workers difficult. The operating characteristics of these instruments suggest that the transversely oscillating files (which may influence clinical performance) are highly susceptible to loading (Walmsley, 1987). This results in the file tip being constrained within the root canal. Clearly, further work is necessary in this area of endosonics to assess adequately the mechanism of action of these instruments. Surgical applications
The ultrasonic descaler has also been adapted for use in dental surgical procedures such as removal of the apical portions of roots of teeth (Richman, 1957) and surgical extraction of teeth (Horton et al., 1981). The clinical advantages of such techniques appear to be related to good haemorrhage control and field visibility. No adverse effects have been reported so far by such uses of ultrasound and healing appears uneventful with minimal patient discomfort. The potential hazards of utilising ultrasonic vibrations in these surgical situations has not been fully assessed. Other dental uses
In conservative dentistry the adapted ultrasonic descaler has been used for the condensation of amalgam restorations (Skinner and Mizera, 1958) together with restoration contouring and elimination of interproximal ledges (Forrest, 1967; Gaffney et al., 1981). The condensation of amalgam restorations in the prepared tooth cavity is a dangerous practice as it may produce increased levels of mercury vapour in the surrounding air (Chandler et al., t971) and should be discouraged. It may also be used during orthodontic treatment to remove interdental contacts between teeth, cemented orthodontic brackets, and superficial decalcification of enamel (Gorelick and Tascher, 1967; Cooke and Wreakes, 1978). The ultrasonic descaler may also be used to remove fractured metal posts from teeth by breaking the cement seal (Krell et al., 1985). DIAGNOSTIC ULTRASOUND The use of ultrasound in the MHz range as a potential clinical diagnostic device has been investigated. Lees ( 1971 ) has demonstrated that it is possible to measure the size and shape of the pulp chamber of
Volume14, Number 1, 1988 teeth using an ultrasound pulse echo system. This has also been used to diagnose areas of early enamel demineralisation following acid attack (Lees et al., 1973). However such diagnostic usage of ultrasound is limited by both the high acoustic impedance mismatches between the various interfaces (enamel, dentine, and pulpal tissues) and the anatomical arrangement and geometry of the tooth. Consequently, it is still at an early stage of development. Other potential uses of diagnostic ultrasound include the mapping out of the oral soft tissues overlying the alveolar bone (Daly and Wheeler, 1971). This technique has been adapted to assess the thickness of the oral mucosa in patients wearing complete dentures (Kydd et al., 1971). Furthermore, Spranger (1971) has shown that diagnostic ultrasound may be used to provide similar information to that obtained from periapical radiographs in the monitoring of periodontal disease. THERAPEUTIC ULTRASOUND Ultrasound in the MHz frequency range has been used therapeutically to the head and neck to treat a variety of inflammatory disorders ranging from temporomandibular joint dysfunction (Esposito et al., 1984) to improving the rate of healing after removal of wisdom teeth (El Hag et al., 1985). The anti-inflammatory effects of such treatment may be largely placebo in action, with the beneficial results related to patient motivation during treatment (Roman 1960; Walmsley, 1984; E1 Hag et al., 1985). Recent work to investigate this placebo effect has utilised the removal of the lower wisdom tooth as a model of acute inflammation. The use of low intensity ultrasound (3 MHz, 0.1 W cm -2, 2 ms pulses with 8 ms spaces, 5 min duration) was found to produce a major placebo effect and this could be related to an inhibition in the release of inflammatory mediators from cells (Hashish et al., 1986). ULTRASONIC CLEANING BATHS Ultrasound is often used commercially in the cleaning of solid objects by the immersion in liquid and subsequent exposure to the mechanical effects of cavitational activity and acoustic microstreaming. This is also applicable in dentistry. Ultrasonic cleaning baths operating at frequencies of 18-100 kHz (Repacholi, 1981 ) are used in dentistry for removing debris from instruments prior to sterilisation (Gordon, 1973), calculus and staining from dentures (Abelson, 1981), and disinfecting rubber base impressions prior to casting (Lorton et al., 1978).
Applications of ultrasound in dentistry • A. D. WALMSLEY
SUMMARY Since its introduction in the early 1950s, ultrasound is now widely used within dentistry. Unfortunately, this increased usage does not appear to have produced any similar awareness of the potential biological hazards of ultrasound (Walmsley, 1988). Other problems exist in that little standardisation of the instruments such as the ultrasonic descaler has been carried out. It is important that such standardisation is carfled out so that the instruments may be used effectively with the minimum of potential damage to associated biological structures.
Acknowledgements--The author
would like to thank Professor W. R. E. Laird and Dr. A. R. Williams for their assistance in the preparation of this article.
REFERENCES Abelson D. C. (1981) Denture plaque and denture cleansers. J. Prosthet. Dent. 45, 376-379. Ahmad M., Pitt Ford T. R. and Crum L. A. (1987) Ultrasonic debridement of root canals: an insight into the mechanisms involved. J. Endodont. 13, 93-101. Aleo J. J., De Renzis F. A., Farber P. A. and Varboncoeur A. P. (1974) The presence of biological activity of cementum bound endotoxin. J. Periodontol. 45, 672-675. Allen D. and Kerr D. (1965) Response in the guinea pig to sterile and non-sterile calculus. J. Periodontol. 36, 121-126. Balamuth L. (1963) Ultrasonics and dentistry. Sound 2, 15-19. Balamuth L. (1967) The application of ultrasonic energy in the dental field. In Ultrasonic Techniques in Biology and Medicine (Edited by B. Brown and D. Gordon), pp. 194-205. II!ife, London. Bhasker S. N., Grower M. F. and Cutright D. E. (1972) Gingival healing after hand and ultrasonic scaling--biochemical and histological analysis. J. Periodontol. 43, 31-34. Burman L. R, Alderman N. E. and Ewen S. J. (1958) Clinical application of ultrasonic vibrations for subgingival calculus and stain removal. J. Dent. Med. 13, 156-161. Catuna M. C. (1953). Sonic energy. A possible dental application. Preliminary report of an ultrasonic cutting method. Ann. Dent. 12, 256-260. Chandler H., Rupp N. and Paffenbarger G. (1971) Poor mercury hygiene from ultrasonic amalgam condensation. Am. Dent. Assoc. J. 82, 553-557. Clark S. M. (1969) The ultrasonic dental unit--a guide for the clinical application of ultrasound in dentistry and dental plaque. Z Periodontol. 40, 621-629. Cooke M. S. and Wreakes G. (1978). Orthodontic decalcification, the ultrasonic scaler and the premade positioner. A new orthodontic triad. Br. J. Ortho. 5, 157-159. Cunningham W. T., Martin H., Pellen G. B. and Stoops D. E. (1982). A comparison of antimicrobial effectiveness of endosonic and hand root canal therapy. Oral Surg. 54, 238-241. Daly C. H. and Wheeler J. B. ( 1971) The use of ultrasonic thickness measurement in the clinical evaluation of the oral soft tissue. Int. Dent. J. 21,418-429. Donz6 Y., Kruger J., Ketterl W. and Rateitschak K. H. (1973) Treatment of gingivitis with Cavitron and hand instruments: A comparative study. Helv. Odontok Acta. 17, 31-37. D'Silva I. V., Nayak R. P., Cherian K. M. and Mulky M. J. (1979). An evaluation of the root topography following periodontal instrumentation--a scanning electron microscope study. J. Periodontol. 50, 283-290.
13
El Hag M., Coghlan K, Christmas P., Harvey W. and Harris M. (1985) The anti-inflammatory effects of dexamethasone and therapeutic ultrasound in oral surgery. Br..L Oral. Surg. 23, 17-23. Esposito C. J., Veal S. J. and Farman A. G. (1984) Alleviation of myofacial pain with ultrasonic therapy. J. Prosthet. Dent. 51, 106-108. Forrest J. O. (1967) Ultrasonic scaling--A five year assessment. Br. Dent. J. 122, 9-14. Frost H. M. (1977) Heating under ultrasonic dental scaling conditions. In Symposium on Biological Effects and Characteristics of Ultrasound Sources. pp. 64-76. U.S. Dept HEW Publication (FDA) 78-8048, Washington, DC. Gaffney J. L., Lehman J. W. and Miles M. J. (1981) Expanded use of the ultrasonic descaler. J. Endodont. 7, 228-229. Goldman H. M. (1961) Histologic assay of healing following ultrasonic curettage versus hand instrument curettage. Oral Surg. 14, 925-928. Gordon P. D. (1973) An ultrasonic cleaner on trial. Dental ~rpdate I, t25-126. Gorelick J. L. and Tascher P. J. (1967). Ultrasonics as an adjunct in orthodontics. N.Y. State Dent. J. 33, 73-82. Griffiths B. M. and Stock C. J. R. (1986) The etficiency of irrigants in removing root canal debris when used with an ultrasonic preparation technique. Int. Endodont. J. 19, 277-284. Hashish 1.. Harvey W. and Harris M. (1986) Anti-inflammatory effects of ultrasound therapy: Evidence for a major placebo effect. Br. J. Rheumatol. 23, 77-81. Hatfield C. G. and Baumhammers A. (1971). Cytotoxic effects of periodontally involved surfaces of human teeth. Arch. Oral Biol. 16, 465-468. Horton J. E., Tarpley T. M., Jr. and Jacoway J. R. (1981) Clinical applications of ultrasonic instrumentation in the surgical removal of bone. Oral Surg. 51,236-241. Jenkins G. N. (1966) The Physiology qf the Mouth, Blackwell, Oxford. Johnson W. N. and Wilson J. R. (1957) Application of the ultrasonic dental unit to scaling procedures. J. Periodontol. 28, 264-271. Jones S. J., Lozdan J. and Boyde A. (1972) Tooth surfaces treated in situ with periodontal instruments--scanning electron microscope studies. Br. Dent. J. 132, 57-64. Krell K. V., Jordan R. D., Madison S. and Aquilerio S. (1985) Using ultrasonic scalers to remove fractured root posts. J. Prosthet. Dent. 55, 46-49. Kydd W. L., Daly C. H. and Wheeler J. B. (1971) The thickness measurement of masticatory mucosa in vivo. Int. Dent. J. 21, 430-441. Lees S. ( 1971 ) Ultrasonics in hard tissues. Int. Dent. J. 21,403-417. Lees S. (1972) Some capabilities of ultrasonics in dental diagnostics and dental research. In Interaction of Ultrasound and Biological Tissues, pp. 281-285. U.S. Dept. HEW Publication (FDA) 78-8048, Washington, DC. Lees S., Gerhard F. B. and Oppenheim F. G. (1973) Ultrasonic measurements of dental enamel demineralization. Ultrasonics 11,269-273. L6e H. (1970) A reivew of the prevention and control of plaque. In Dental Plaque (Edited by W. D. McHugh) Livingstone, Edinburgh. L6e H., Theilade E. and Jensen S. B. (1965) Experimental gingivitis in man. J. Periodontol. 36, 177-187. Lorton L., Phillips R. W. and Schwartz M. L. (1978) The effect of ultrasonic cleaning methods on rubber base impression materials. J. Dent. Res. 57, 939. Martin H. (1976) Ultrasonic disinfection of the root canal. Oral Surg. 42, 92-99. Martin H., Cunningham W. T., Norris J. P. and Cotton W. R. (1980) Ultrasonic versus hand filing of dentin: a quantitative study. Oral Surg. 49, 79-81. McCall C. M., Jr. and Szmyd L. (1960) Clinical evaluation of ultrasonic scaling. 31 Am. Dent. Assoc. 61,559-564. McHugh W. D. (1970)Dental Plaque. Livingstone, Edinburgh.
14
Ultrasound in Medicine and Biology
Moskow B. S. and Bressman E. (1964) Cemental response to ultrasonic and hand instrumentation. J. Am. Dent. Assoc. 68, 698-703. Nehammer C. F. and Stock C. J. R. (1985) Preparation and filling of the root canal. Br. Dent. J. 158, 285-291. Nielsen A. G. and Richards J. R. (1954) Application of ultrasonics to the cutting of teeth. J. Dent. Res. 33, 698. Nishimine D. and O'Leary T. J. (1979) Hand instrumentation versus ultrasonics in the removal of endotoxins from root surfaces. J. Periodontol. 50, 345-349. Oman C. R. and Applebaum E. (1955) Ultrasonic cavity preparation II. Progress report. J. Am. Dent. Assoc. 50, 414-417. Postle H. H. (1958) Ultrasonic cavity preparation. J. Prosthet. Dent. 8, 153-160. Repacfioli M. H. ( 1981 ) Ultrasound. Characteristics and Biological Action. National Research Council of Canada, Ottawa, NRCC 19244. Richman M. J. (1957) The use of ultrasonics in root canal therapy and root resection. J. Dent. Med. 12, 12-18. Robinson P. (1975) Possible roles of diseases cementum in periodontics. J. Prey. Dent. 2, 3-5. Roche H. A. P. (1954) Ultrasonic drill. Br. Dent. J. 97, 96-98. Roman M. P. (1960) A clinical evaluation of ultrasound by use of a placebo technique. Phys. Ther. Rev. 40, 649-652. Rosenberg R. M. and Ash M. M., Jr. (1974) The effect of root roughness on plaque accumulation and gingival inflammation. J. Periodontol. 45, 146-150. Sanderson A. D. (1966) Gingival curettage by hand and ultrasonic instruments--a histologic comparison. J. Periodontol. 37, 279-290. Schaffer E. M., Stende G. and King D. (1964) Healing periodontal pocket tissues following ultrasonic scaling and hand planing. J. PeriodontoL 35, 140-148. Schaffer E. M. (1967) Periodontal instrumentation--scaling and root planing. Int. Dent. J. 17, 297-319. Schroeder H. E. (1969) Formation and Inhibition o f Dental Calculus. Hans Huber, Berne, Switzerland. Skinner E. W. and Mizera G. T. (1958) Condensation of amalgam with ultrasonic vibration. J. Prosthet. Dent. 8, 183-194. Spranger H. (1971) Ultrasonic diagnosis of marginal periodontal disease. Int. Dent. J. 21,442-445.
Volume 14, Number 1, 1988 Stende G. W. and Schaffer E. M. ( 1961) A comparison of ultrasonic and hand scaling. J. Periodontol. 32, 312-314. Stewart J. L., Drisko R. R. and Herlach A. D. (1967) Comparison of ultrasonic and hand instruments for the removal of calculus. J. Am. Dent. Assoc. 75, 153-157. Street E. V. (1959) Critical evaluation of ultrasonics in dentistry. J. Prosthet. Dent. 9, 132-141. Suppipat N. (1974) Ultrasonics in periodontics. J. Clin. Periodontol. 1,206-213. Torfason T., Kiger R., Seling K. A. and Egelberg J. (1979) Clinical improvement of gingival conditions following ultrasonics versus hand instrumentation of periodontal pockets. J. C\lin. Periodontol. 6, 165-176. Walmsley A. D. (1984) Alleviation of myofacial pain with ultrasonic therapy (letter). J. Prosthet. Dent. 52, 312. Walmsley A. D. (1987) Endosonics: the need for scientific evaluation. Int. Endodont. J. 20, 105-111. Walmsley A. D. (1988) Potential hazards of the dental ultrasonic descaler. Ultrasound in Med. & Biol. 14, 000-000. Walmsley A. D., Laird W. R. E. and Williams A. R. (1984) A model system to demonstrate the role ofcavitational activity in ultrasonic scaling. J. Dent. Res. 63, 1162-1165. Walmsley A. D., Laird W. R. E. and Williams A. R. (1986a) Displacement amplitude as a measure of the acoustic output of ultrasonic scalers. Dent. Mater. 2, 97-100. Walmsley A. D., Laird W. R. E. and Williams A. R. (1986b). Inherent variability of the performance of the ultrasonic descaler. J. Dent. 14, 121-125. Walsh T. F. and Waite I. M. (1978) A comparison of post-surgical healing following debridement by ultrasonic or hand instruments. J. Periodontol. 49, 201-205. Wells P. N. T. (1977) Biomedical Ultrasonics. Academic Pres, London. Williams A. R. (1983) Ultrasound: biological effects and potential hazards. Academic Press, London. Wilson J. R. (1958) The use of ultrasonics in periodontal treatment. J. Prosthet. Dent. 8, 161-166. Zinner D. D. (1955) Recent ultrasonic dental studies including periodontia, without the use of an abrasive. J. Dent. Res. 34, 748-749.
0301-5629/88 $3.00 + .00 © 1987 Pergamon Journals Ltd.
OOriginal Contribution APPLICATIONS
OF ULTRASOUND
IN DENTISTRY
A. D. W A L M S L E Y Department of Dental Prosthetics, The Dental School, St. Chad's Queensway, Birmingham, B4 6NN (Received 11 February 1987; in revisedforrn 29 May 1987) Abstract--An ultrasonic descaler working at kHz frequencies is used in dentistry to remove attached deposits from the teeth. Such devices offer many advantages over conventional hand instruments by reducing both the work and time involved in the clinical descaling process. Although it is a recognised clinical instrument, there has been little attempt to standardise its acoustic power output. A parameter which may characterise adequately the acoustic emission from these instruments is the displacement amplitude of the probe tip. Modification of the ultrasonic descaler generator has led to the further use of the instrument in other dental areas. Diagnostic applications of M H z ultrasound is limited by the structure and arrangement of the dental tissues. Therapeutic ultrasound has been used to treat a variety of dentally related ailments, and ultrasonic cleaning baths are used to clean both dental instruments and materials.
Key Words: Ultrasound, Dentistry, Clinical applications.
INTRODUCTION The common perception of the use of ultrasound from a medical point of view is in its wide use in areas such as diagnostic imaging and physiotherapy. Within the wider aspects of medicine however ultrasound finds considerable uses in the practice of dentistry. One of the earliest references to its use in the dental sphere was in 1952, where an industrial ultrasonic impact grinder was used to prepare cavities in extracted h u m a n teeth (Balamuth, 1963). This quickly caught the imagination of dentists and the potential use of such an ultrasonic dental drill was reported by Catuna (1953), with aa instrument being introduced eventually for cavity preparation in the teeth of patients (Nielsen and Richards, 1954; Roche, 1954; Oman and Applebaum, 1955). These early instruments operated at a frequency of around 29 kHz using an abrasive slurry ofaluminium oxide particles to assist in the cutting process. Tooth substance was removed efficiently by this technique (Postle, 1958). There was little patient discomfort and it was suggested that cavity preparation could be performed without recourse to local anaesthesia. Furthermore, as a low contact load was employed in cutting, potential traumatic effects on the underlying vascular and nervous tissues of the dental pulp were reduced. However, ultrasonic cavity preparation never became popular due to poor visual access and the large
amount of aluminium slurry used during cutting which required removal. As a result it was superseded by the more effective high speed rotary drills (Street, 1959) which were developed around the same time. The role of ultrasonics in dentistry did not disappear altogether since previously Zinner (1955) had adapted the original ultrasonic drill for use in the removal of dental plaque and calculus from the surface of the teeth (descaling). This process was first demonstrated clinically by Johnson and Wilson (1957) and is now a widely accepted clinical procedure. By the seventies it was reported that within the United States of America there were some 50,000 to 100,000 ultrasonic devices in use for descaling and periodontal treatment (Lees, 1972; Frost, 1977). At the present time the number of units is likely to be far in excess of this number worldwide although accurate figures do not exist. The use of ultrasound in dentistry is not restricted to the descaling of teeth, however, and its application in other areas has been steadily increasing (Balamuth, 1967). The ultrasonic descaler has been modified for use also in root canal therapy (endodontics), amalgam packing, extraction of teeth, and displacing cemented restorations from teeth. Other applications of ultrasound in dentistry include the treatment of joint and muscle related ailments around the face, the generalised cleaning of both instruments prior to sterilisation and dentures, and as a
8
Ultrasound in Medicineand Biology
Volume14, Number 1, 1988
diagnostic procedure to detect dental caries and periodontal disease. ULTRASONIC DESCALING The supporting tissues of the natural human tooth (Fig. 1) consist of the gingivae, the periodontal ligament, and the alveolar bone, collectively termed the periodontium. These tissues may be subject to inflammatory change which, if left untreated may lead to irreversible damage with subsequent loss of the teeth. The primary etiological factor in periodontal disease is the deposition and accumulation of dental plaque on the surfaces of teeth (Lre et at., 1965). Dental plaque is a soft tenacious bacterial deposit which forms on the surface of a tooth when oral hygiene methods are ineffective or abandoned (McHugh, 1970), and the control of plaque formation and its effective removal is an essential requiremetn for periodontal health (Lre, 1970). If dental plaque is allowed to accumulate, deposition of calcium salts in its matrix will result in the formation of dental calculus, which consists mainly of 80% inorganic matter mainly in the form of calcium phosphate as hydroxyapatite, and inorganic matter comprising mainly desquamated epithelial cells and bacteria (Jenkins, 1966). Calculus acts as tissue irritant by virtue of its roughness, bacterial content, and by the accumulation of further dental plaque deposits on its surface (Allen and Kerr, 1965; Schroeder, 1969). The main application of ultrasound in dentistry therefore is to remove both dental plaque and cal-
~
Gn i gvia P i de onnttal Lg iearo m
~
Enamel
I~
Pupl Denn tie
Root
Cemenu tm A v l e o a l Bone r Fig. 1. A schematic diagram of the constituents of the tooth and its supporting tissue.
Fig. 2. The ultrasonic descaler being used clinically to remove attached deposits from the surfaces of the teeth.
culus deposits from the surfaces of teeth (Fig. 2) using an ultrasonic descaler (Suppipat, 1974). These instruments operate at frequencies of 25-42 kHz and are useful in that they reduce the mechanical effort required by the clinician. Furthermore they are easy to operate and there is a reduction in both the treatment time and the level of discomfort to the patient. These devices utilise a rigid metal probe which is driven to oscillate in its longitudinal mode. It is this vibratory motion that provides the "chipping" action which removes the attached deposits from the teeth. A magnetostrictive or a piezoelectric transducer within the handpiece is used to produce the ultrasonic vibrations. In magnetostrictive designs, the metal probe is attached to a laminated ferromagnetic stack (Fig. 3a). Each probe has its own integral stack being known as an "insert" and this is powered by the same generator via coils in the handpiece. Piezoelectric devices are much simpler in design in that the different probes are interchangeable with the one transducer. Both designs utilise a flow of cooling water which is passed through the handpiece and onto the oscillating tip. The cooling water serves to reduce frictional heating at the tooth/tip interface and in magnetostrictive transducers it also is used to cool the ferromagnetic stack. On reaching the tip, cavitational activity occurs within the water (Walmsley et al., 1986a), and thus may also contribute to the removal of the attached deposits (Balamuth 1967; Walmsley et al., 1984). A variety of probe tip designs are used in the descaling process and examples of the more commonly used probes are shown in Fig. 3b. They range from straight or sickle probe tips approximately 2-3 cm long and 0.2 cm broad at the tip to angled/blade designs incorporating a 0.5 by 1 cm blade tip. Such designs are used for different clinical tasks such as
Applications of ultrasound in dentistry • A. D. WALMSLEY
(a)
(b)
Fig. 3(a). An example of inserts for a magnetostrictive generator are shown; (b) Three commonly used designs of descaling probe tips: A, straight; B, angled blade, and C, sickle. general descaling and root planing (which will be discussed below). They are all based on conventional hand-held instrument designs as it is assumed by both manufacturers and clinicians that both forms of descaling achieve the same result. During oscillation, clinicians anticipate that the oscillatory movement of the descaling tip will occur along the longitudinal axis of the instrument (Johnson & Wilson, 1957). The direction of oscillation observed, however invariably occurs at an angle O to the longitudinal axis of the instrument (Fig. 4). This angle is approximately 5 ° for the straight probe designs and 30 ° for sickle/angled designs (Walmsley el al., 1986b). Although most designs exhibit a true longitudinal motion, some of the more complex probe tips demonstrate an open elliptical motion. Comparison to conventional instrumentation Although ultrasonic descaling is effective in the removal of dental plaque and calculus, the use of
9
hand instruments may also achieve similar clinical results. Therefore the majority of clinical investigations in relation to the ultrasonic descaler have been concerned with its efficiency when compared to manual methods and to assess which, if any, is superior. Clinical studies on the quality of the descaling process show that both manual and ultrasonic instrumentation remove the attached calculus from the tooth surface efficiently with no apparent differences between either technique (McCall and Szmyd, 1960; Stende and Schaffer, 1961; Moskow and Bressman, 1964). These initial findings were followed by scanning electron microscope studies of the enamel and dentinal surfaces following routine descaling procedures. This suggested that ultrasonic devices tended to remove the calculus in small fragments with burnishing of the remaining deposits, whilst hand instruments removed the calculus in much larger fragments (Jones et al., 1972). However, calculus removal by the ultrasonic descaler was superior from those teeth where there was good access. In patients suffering from periodontal disease there is often a surface layer of necrotic cementum overlying the root. This necrotic cementum contains bacterial products which may be irritant to the periodontal tissues (Hatfield and Baumhammers, 1971; Aleo et al.. 1974) and the removal of this surface layer of cementum (root planing) is an established part of the descaling process (Rosenberg and Ash, 1974; Robinson, 1975). After a course of descaling and root planing, Torfason et al. (1979) showed that both hand and ultrasonic instrumentation produced similar rates of resolution of inflamed periodontal tissues. However, this result has been disputed by Nishimine and O'Leary (1979) who reported that, in root planing, hand instruments were superior to ultrasonic descalers. A generalised conclusion from the above studies is that for either root planing or areas of the mouth where access is difficult, ultrasonic descalers are relatively ineffective (Stende and Schaffer, 1961; Suppipat, 1974; Nishimine and O'Leary, 1979) and a further course of descaling with hand instruments is usually required to achieve a clinically satisfactory
Longitudinal Axis
Fig. 4. A diagrammatic representation of the probe oscillations which occur at an angle (O) to the longitudinal axis of the instrument.
10
Ultrasound in Medicineand Biology
result. This is generally related to both the lack of operator tactile sensitivity when utilising the instrument and poor visibility created by the associated aerosol spray. The efficiency of any descaling technique may also be assessed by the eventual healing and resolution of the periodontal tissues. In clinical studies, most investigators agree that tissues surrounding teeth that are subjected to ultrasonic descaling show more rapid resolution to health, as demonstrated by a larger reduction in the tissue inflammation, than where a hand instrument was used (Goldman, 1961 ; Schaffer et al., 1964; Sanderson, 1966; Walsh and Waite, 1978). This may be due to an increased rate of collagen production stimulated by the ultrasonic descaler (Bhasker et al., 1972). However, at these frequencies the effect of the ultrasound may chiefly be hormetic (Williams, 1983), that is, a beneficial or stimulating effect resulting from the application of a small "dose" of a harmful or irritating agent. Generally, most investigators cite the presence of a water spray, with its lavage action irrigating the tissues, as the major reason for the superiority of the ultrasonic descaler (Clark, 1969; Bhasker, et al., 1972; D'Silva et al., 1979). However, no consideration was given in any of the above reports to the role of cavitational activity within that water supply and its potential cleaning action. Clinical evaluation
The main advantage claimed for the use of an ultrasonic descaler is that calculus removal is accomplished more rapidly than with conventional hand instruments (Johnson and Wilson, 1957; Torafason et al., 1979) and time savings of 20% (Forrest, 1967) to 50% (Donz~ et al., 1973) have also been reported. However, it appears that for efficient removal of calculus, the same amount of time is involved regardless of the technique used (Burman et al., 1958), although ultrasonic descaling may be quicker for mandibular teeth (Stewart et al., 1967). During clinical treatment the majority of patients appear to prefer ultrasonic descaling to hand instrumentation (Johnson and Wilson, 1957; Forrest, 1967; Donz6 et al., 1973) and this may be attributed to a reduction in discomfort (Johnson and Wilson, 1957). Clearly this is an advantage in situations where the tissues may be unduly susceptible to pain in the presence of infection (Wilson, 1958). In addition, many clinicians prefer using the ultrasonic descaler (Stewart et al., 1967) which may be related to a reduction in both physical effort and complex manipulation. However, the possible loss of tactile sensation when using the device makes it diffi-
Volume14, Number 1, 1988 cult to be sure that all calculus has been removed completely, a problem that does not appear to exist when using hand instruments (Burman et al., 1958; Moskow and Bressman, 1964; Schaffer, 1967). I n s t r u m e n t standardisation
Many investigations into the performance of the ultrasonic descaler, may be criticised due to the fact that there was inadequate standardisation of the operating instrument. The clinical settings of the working ultrasonic descaler have ranged from the use of either "medium" or "high" power levels used in conjunction with a free flow of water (Moskow and Bressman, 1964; Jones et al., 1972; D'Silva et al., 1979) to a power setting and flow of cooling water adjusted to the "operator's preference" with the precise conditions not being reported (Sanderson, 1966; Torfason et al., 1979). Some investigators gave no details of the working conditions of their instrument (McCall and Szmyd, 1960; Goldman, 1961; Stende and Schaffer, 1961; Donz~ et al., 1973). Other variables which are not adequately described are the time spent and the application loads used during operation. Interpretation and comparison of the results obtained from different workers is difficult, therefore, due to these discrepancies in the instrument standardisation. Although there are various methods used to measure the acoustic power output emitted from medical transducers operating at MHz frequencies (Wells, 1977), there is no commonly agreed technique used for representing the power output from ultrasonic descalers working in the kHz range. The majority of these instruments are designed with a control dial enabling the operator to vary the amount of electrical power input to the transducer, and an estimate of this is displayed on an arbitrary linear scale. This scale, however does not provide a meaningful estimate of any relevant acoustic emission from the probe tip. A parameter which adequately characterises the acoustic emission is the displacement amplitude of the oscillating tip (Walmsley et al., 1986a). The displacement amplitude may be measured using a travelling light microscope at an overall magnification of 100×. This provides a direct measure of the "chipping" action of the probe tip when used clinically. Displacement amplitudes for the descaling tips range from 18-27 gm for straight probes and from 27-65 um for sickle probes (Walmsley et al., 1986b). It has been shown that differing designs of the descaling tip exhibit different displacement amplitudes at the same nominal power output from the same generator. Furthermore, different generators from the
Applications of ultrasound in dentistry • A. D. WALMSLFY
same manufacturer produce a different range of displacement amplitudes when the same probe design is used (Walmsley et al., 1986b). The displacement amplitude not only gives a measure of the amount of"chipping" action but also gives a direct measure of cavitational activity occurring within the associated cooling water (Walmsley et al., 1986a). When measured by chemical dosimetry methods, an apparent "threshold" for the onset of cavitational activity occurs at displacement amplitude of 12 um. It is then found to increase in a linear manner with increasing displacement amplitude of the probe (Walmsley et al., 1986a). A measure &electrical power input to the transducer is meaningless (using the manufacturers control dial) because the transduction process is inefficient. This is demonstrated by a nonlinear increase in the displacement amplitude with increasing power setting (Walmsley et al., 1986a; 1986b). As the displacement amplitude appears to be a satisfactory method of determining the efficiency of an ultrasonic descaling tip, measurements for the individual probes in relation to acoustic power output should be displayed in manufacturers literature. This is necessary in order to regularize and improve clinical performance and allow meaningful comparison of results between different clinical investigators.
11
file (Fig. 5). This oscillating file is placed within the root canal of the tooth and abrades the walls removing contaminated organic and inorganic material. An antiseptic solution (usually sodium hypochlorite) is often passed over the oscillating tip to aid in the cleaning process (Cunningham et al., 1982; Griffiths and Stock, 1986). The occurrence of acoustic microstreaming fields developed around small irregularities protruding from the file surface increases the effectiveness of the disinfectant (Ahmad et al., 1987). Cavitational activity has been shown not to occur along the oscillating file and this is probably related to the relatively low displacement amplitudes produced when it is oscillating within the canal (Ahmad et al., 1987). These instruments have been subject to investi-
(a) L
T
MODIFICATIONS OF THE ULTRASONIC DESCALER Apart from the routine descaling procedures, the basic principles of the ultrasonic descaler have found use in other areas of dentistry. Generally the generator remains unchanged but different shaped inserts are used to perform the particular clinical task that is required. Endodontics Ultrasonic vibrations may be used to prepare and clean the root canal of nonvital teeth before filling is commenced (Richman, 1957; Martin, 1976; Nehammer and Stock, 1985). The development of such instruments was pioneered by Martin in the early 1970s (Martin, 1976) and is now a well recognised and documented technique which is rapidly growing in popularity. These instruments are essentially a direct adaptation of the ultrasonic descaler where a rigid metal rod is driven to oscillate in its longitudinal mode. However, unlike the descaling instruments, a small file is attached near the end of the main driver and is set at an angle of 60-90 ° to the main longitudinal axis. Accordingly, during operation a transverse wave is set up along the length of the
Fig. 5(a). A diagrammatic representation of the ultrasonic endodontic instrument showing the main longitudinal oscillation (L) occurring along the main axis. The metal file is at right angles to the main instrument and a transverse oscillation (T) is set up along its length; (b) The transverse oscillation of the metal file consists of nodes (N) and antinodes (A). The tip of the file being unconstrained exhibits a large oscillation (from Walmsley, 1987).
12
Ultrasound in Medicineand Biology
gations which are mainly related to the clinical efficiency of the instrument. The advantages claimed for such treatment over conventional methods include cleaner root canals with increased debris removal and a reduction in bacterial contamination (Martin et al., 1980; Cunningham et al., 1982). The majority of investigators have not adequately standardised their instruments, making comparison between different workers difficult. The operating characteristics of these instruments suggest that the transversely oscillating files (which may influence clinical performance) are highly susceptible to loading (Walmsley, 1987). This results in the file tip being constrained within the root canal. Clearly, further work is necessary in this area of endosonics to assess adequately the mechanism of action of these instruments. Surgical applications
The ultrasonic descaler has also been adapted for use in dental surgical procedures such as removal of the apical portions of roots of teeth (Richman, 1957) and surgical extraction of teeth (Horton et al., 1981). The clinical advantages of such techniques appear to be related to good haemorrhage control and field visibility. No adverse effects have been reported so far by such uses of ultrasound and healing appears uneventful with minimal patient discomfort. The potential hazards of utilising ultrasonic vibrations in these surgical situations has not been fully assessed. Other dental uses
In conservative dentistry the adapted ultrasonic descaler has been used for the condensation of amalgam restorations (Skinner and Mizera, 1958) together with restoration contouring and elimination of interproximal ledges (Forrest, 1967; Gaffney et al., 1981). The condensation of amalgam restorations in the prepared tooth cavity is a dangerous practice as it may produce increased levels of mercury vapour in the surrounding air (Chandler et al., t971) and should be discouraged. It may also be used during orthodontic treatment to remove interdental contacts between teeth, cemented orthodontic brackets, and superficial decalcification of enamel (Gorelick and Tascher, 1967; Cooke and Wreakes, 1978). The ultrasonic descaler may also be used to remove fractured metal posts from teeth by breaking the cement seal (Krell et al., 1985). DIAGNOSTIC ULTRASOUND The use of ultrasound in the MHz range as a potential clinical diagnostic device has been investigated. Lees ( 1971 ) has demonstrated that it is possible to measure the size and shape of the pulp chamber of
Volume14, Number 1, 1988 teeth using an ultrasound pulse echo system. This has also been used to diagnose areas of early enamel demineralisation following acid attack (Lees et al., 1973). However such diagnostic usage of ultrasound is limited by both the high acoustic impedance mismatches between the various interfaces (enamel, dentine, and pulpal tissues) and the anatomical arrangement and geometry of the tooth. Consequently, it is still at an early stage of development. Other potential uses of diagnostic ultrasound include the mapping out of the oral soft tissues overlying the alveolar bone (Daly and Wheeler, 1971). This technique has been adapted to assess the thickness of the oral mucosa in patients wearing complete dentures (Kydd et al., 1971). Furthermore, Spranger (1971) has shown that diagnostic ultrasound may be used to provide similar information to that obtained from periapical radiographs in the monitoring of periodontal disease. THERAPEUTIC ULTRASOUND Ultrasound in the MHz frequency range has been used therapeutically to the head and neck to treat a variety of inflammatory disorders ranging from temporomandibular joint dysfunction (Esposito et al., 1984) to improving the rate of healing after removal of wisdom teeth (El Hag et al., 1985). The anti-inflammatory effects of such treatment may be largely placebo in action, with the beneficial results related to patient motivation during treatment (Roman 1960; Walmsley, 1984; E1 Hag et al., 1985). Recent work to investigate this placebo effect has utilised the removal of the lower wisdom tooth as a model of acute inflammation. The use of low intensity ultrasound (3 MHz, 0.1 W cm -2, 2 ms pulses with 8 ms spaces, 5 min duration) was found to produce a major placebo effect and this could be related to an inhibition in the release of inflammatory mediators from cells (Hashish et al., 1986). ULTRASONIC CLEANING BATHS Ultrasound is often used commercially in the cleaning of solid objects by the immersion in liquid and subsequent exposure to the mechanical effects of cavitational activity and acoustic microstreaming. This is also applicable in dentistry. Ultrasonic cleaning baths operating at frequencies of 18-100 kHz (Repacholi, 1981 ) are used in dentistry for removing debris from instruments prior to sterilisation (Gordon, 1973), calculus and staining from dentures (Abelson, 1981), and disinfecting rubber base impressions prior to casting (Lorton et al., 1978).
Applications of ultrasound in dentistry • A. D. WALMSLEY
SUMMARY Since its introduction in the early 1950s, ultrasound is now widely used within dentistry. Unfortunately, this increased usage does not appear to have produced any similar awareness of the potential biological hazards of ultrasound (Walmsley, 1988). Other problems exist in that little standardisation of the instruments such as the ultrasonic descaler has been carried out. It is important that such standardisation is carfled out so that the instruments may be used effectively with the minimum of potential damage to associated biological structures.
Acknowledgements--The author
would like to thank Professor W. R. E. Laird and Dr. A. R. Williams for their assistance in the preparation of this article.
REFERENCES Abelson D. C. (1981) Denture plaque and denture cleansers. J. Prosthet. Dent. 45, 376-379. Ahmad M., Pitt Ford T. R. and Crum L. A. (1987) Ultrasonic debridement of root canals: an insight into the mechanisms involved. J. Endodont. 13, 93-101. Aleo J. J., De Renzis F. A., Farber P. A. and Varboncoeur A. P. (1974) The presence of biological activity of cementum bound endotoxin. J. Periodontol. 45, 672-675. Allen D. and Kerr D. (1965) Response in the guinea pig to sterile and non-sterile calculus. J. Periodontol. 36, 121-126. Balamuth L. (1963) Ultrasonics and dentistry. Sound 2, 15-19. Balamuth L. (1967) The application of ultrasonic energy in the dental field. In Ultrasonic Techniques in Biology and Medicine (Edited by B. Brown and D. Gordon), pp. 194-205. II!ife, London. Bhasker S. N., Grower M. F. and Cutright D. E. (1972) Gingival healing after hand and ultrasonic scaling--biochemical and histological analysis. J. Periodontol. 43, 31-34. Burman L. R, Alderman N. E. and Ewen S. J. (1958) Clinical application of ultrasonic vibrations for subgingival calculus and stain removal. J. Dent. Med. 13, 156-161. Catuna M. C. (1953). Sonic energy. A possible dental application. Preliminary report of an ultrasonic cutting method. Ann. Dent. 12, 256-260. Chandler H., Rupp N. and Paffenbarger G. (1971) Poor mercury hygiene from ultrasonic amalgam condensation. Am. Dent. Assoc. J. 82, 553-557. Clark S. M. (1969) The ultrasonic dental unit--a guide for the clinical application of ultrasound in dentistry and dental plaque. Z Periodontol. 40, 621-629. Cooke M. S. and Wreakes G. (1978). Orthodontic decalcification, the ultrasonic scaler and the premade positioner. A new orthodontic triad. Br. J. Ortho. 5, 157-159. Cunningham W. T., Martin H., Pellen G. B. and Stoops D. E. (1982). A comparison of antimicrobial effectiveness of endosonic and hand root canal therapy. Oral Surg. 54, 238-241. Daly C. H. and Wheeler J. B. ( 1971) The use of ultrasonic thickness measurement in the clinical evaluation of the oral soft tissue. Int. Dent. J. 21,418-429. Donz6 Y., Kruger J., Ketterl W. and Rateitschak K. H. (1973) Treatment of gingivitis with Cavitron and hand instruments: A comparative study. Helv. Odontok Acta. 17, 31-37. D'Silva I. V., Nayak R. P., Cherian K. M. and Mulky M. J. (1979). An evaluation of the root topography following periodontal instrumentation--a scanning electron microscope study. J. Periodontol. 50, 283-290.
13
El Hag M., Coghlan K, Christmas P., Harvey W. and Harris M. (1985) The anti-inflammatory effects of dexamethasone and therapeutic ultrasound in oral surgery. Br..L Oral. Surg. 23, 17-23. Esposito C. J., Veal S. J. and Farman A. G. (1984) Alleviation of myofacial pain with ultrasonic therapy. J. Prosthet. Dent. 51, 106-108. Forrest J. O. (1967) Ultrasonic scaling--A five year assessment. Br. Dent. J. 122, 9-14. Frost H. M. (1977) Heating under ultrasonic dental scaling conditions. In Symposium on Biological Effects and Characteristics of Ultrasound Sources. pp. 64-76. U.S. Dept HEW Publication (FDA) 78-8048, Washington, DC. Gaffney J. L., Lehman J. W. and Miles M. J. (1981) Expanded use of the ultrasonic descaler. J. Endodont. 7, 228-229. Goldman H. M. (1961) Histologic assay of healing following ultrasonic curettage versus hand instrument curettage. Oral Surg. 14, 925-928. Gordon P. D. (1973) An ultrasonic cleaner on trial. Dental ~rpdate I, t25-126. Gorelick J. L. and Tascher P. J. (1967). Ultrasonics as an adjunct in orthodontics. N.Y. State Dent. J. 33, 73-82. Griffiths B. M. and Stock C. J. R. (1986) The etficiency of irrigants in removing root canal debris when used with an ultrasonic preparation technique. Int. Endodont. J. 19, 277-284. Hashish 1.. Harvey W. and Harris M. (1986) Anti-inflammatory effects of ultrasound therapy: Evidence for a major placebo effect. Br. J. Rheumatol. 23, 77-81. Hatfield C. G. and Baumhammers A. (1971). Cytotoxic effects of periodontally involved surfaces of human teeth. Arch. Oral Biol. 16, 465-468. Horton J. E., Tarpley T. M., Jr. and Jacoway J. R. (1981) Clinical applications of ultrasonic instrumentation in the surgical removal of bone. Oral Surg. 51,236-241. Jenkins G. N. (1966) The Physiology qf the Mouth, Blackwell, Oxford. Johnson W. N. and Wilson J. R. (1957) Application of the ultrasonic dental unit to scaling procedures. J. Periodontol. 28, 264-271. Jones S. J., Lozdan J. and Boyde A. (1972) Tooth surfaces treated in situ with periodontal instruments--scanning electron microscope studies. Br. Dent. J. 132, 57-64. Krell K. V., Jordan R. D., Madison S. and Aquilerio S. (1985) Using ultrasonic scalers to remove fractured root posts. J. Prosthet. Dent. 55, 46-49. Kydd W. L., Daly C. H. and Wheeler J. B. (1971) The thickness measurement of masticatory mucosa in vivo. Int. Dent. J. 21, 430-441. Lees S. ( 1971 ) Ultrasonics in hard tissues. Int. Dent. J. 21,403-417. Lees S. (1972) Some capabilities of ultrasonics in dental diagnostics and dental research. In Interaction of Ultrasound and Biological Tissues, pp. 281-285. U.S. Dept. HEW Publication (FDA) 78-8048, Washington, DC. Lees S., Gerhard F. B. and Oppenheim F. G. (1973) Ultrasonic measurements of dental enamel demineralization. Ultrasonics 11,269-273. L6e H. (1970) A reivew of the prevention and control of plaque. In Dental Plaque (Edited by W. D. McHugh) Livingstone, Edinburgh. L6e H., Theilade E. and Jensen S. B. (1965) Experimental gingivitis in man. J. Periodontol. 36, 177-187. Lorton L., Phillips R. W. and Schwartz M. L. (1978) The effect of ultrasonic cleaning methods on rubber base impression materials. J. Dent. Res. 57, 939. Martin H. (1976) Ultrasonic disinfection of the root canal. Oral Surg. 42, 92-99. Martin H., Cunningham W. T., Norris J. P. and Cotton W. R. (1980) Ultrasonic versus hand filing of dentin: a quantitative study. Oral Surg. 49, 79-81. McCall C. M., Jr. and Szmyd L. (1960) Clinical evaluation of ultrasonic scaling. 31 Am. Dent. Assoc. 61,559-564. McHugh W. D. (1970)Dental Plaque. Livingstone, Edinburgh.
14
Ultrasound in Medicine and Biology
Moskow B. S. and Bressman E. (1964) Cemental response to ultrasonic and hand instrumentation. J. Am. Dent. Assoc. 68, 698-703. Nehammer C. F. and Stock C. J. R. (1985) Preparation and filling of the root canal. Br. Dent. J. 158, 285-291. Nielsen A. G. and Richards J. R. (1954) Application of ultrasonics to the cutting of teeth. J. Dent. Res. 33, 698. Nishimine D. and O'Leary T. J. (1979) Hand instrumentation versus ultrasonics in the removal of endotoxins from root surfaces. J. Periodontol. 50, 345-349. Oman C. R. and Applebaum E. (1955) Ultrasonic cavity preparation II. Progress report. J. Am. Dent. Assoc. 50, 414-417. Postle H. H. (1958) Ultrasonic cavity preparation. J. Prosthet. Dent. 8, 153-160. Repacfioli M. H. ( 1981 ) Ultrasound. Characteristics and Biological Action. National Research Council of Canada, Ottawa, NRCC 19244. Richman M. J. (1957) The use of ultrasonics in root canal therapy and root resection. J. Dent. Med. 12, 12-18. Robinson P. (1975) Possible roles of diseases cementum in periodontics. J. Prey. Dent. 2, 3-5. Roche H. A. P. (1954) Ultrasonic drill. Br. Dent. J. 97, 96-98. Roman M. P. (1960) A clinical evaluation of ultrasound by use of a placebo technique. Phys. Ther. Rev. 40, 649-652. Rosenberg R. M. and Ash M. M., Jr. (1974) The effect of root roughness on plaque accumulation and gingival inflammation. J. Periodontol. 45, 146-150. Sanderson A. D. (1966) Gingival curettage by hand and ultrasonic instruments--a histologic comparison. J. Periodontol. 37, 279-290. Schaffer E. M., Stende G. and King D. (1964) Healing periodontal pocket tissues following ultrasonic scaling and hand planing. J. PeriodontoL 35, 140-148. Schaffer E. M. (1967) Periodontal instrumentation--scaling and root planing. Int. Dent. J. 17, 297-319. Schroeder H. E. (1969) Formation and Inhibition o f Dental Calculus. Hans Huber, Berne, Switzerland. Skinner E. W. and Mizera G. T. (1958) Condensation of amalgam with ultrasonic vibration. J. Prosthet. Dent. 8, 183-194. Spranger H. (1971) Ultrasonic diagnosis of marginal periodontal disease. Int. Dent. J. 21,442-445.
Volume 14, Number 1, 1988 Stende G. W. and Schaffer E. M. ( 1961) A comparison of ultrasonic and hand scaling. J. Periodontol. 32, 312-314. Stewart J. L., Drisko R. R. and Herlach A. D. (1967) Comparison of ultrasonic and hand instruments for the removal of calculus. J. Am. Dent. Assoc. 75, 153-157. Street E. V. (1959) Critical evaluation of ultrasonics in dentistry. J. Prosthet. Dent. 9, 132-141. Suppipat N. (1974) Ultrasonics in periodontics. J. Clin. Periodontol. 1,206-213. Torfason T., Kiger R., Seling K. A. and Egelberg J. (1979) Clinical improvement of gingival conditions following ultrasonics versus hand instrumentation of periodontal pockets. J. C\lin. Periodontol. 6, 165-176. Walmsley A. D. (1984) Alleviation of myofacial pain with ultrasonic therapy (letter). J. Prosthet. Dent. 52, 312. Walmsley A. D. (1987) Endosonics: the need for scientific evaluation. Int. Endodont. J. 20, 105-111. Walmsley A. D. (1988) Potential hazards of the dental ultrasonic descaler. Ultrasound in Med. & Biol. 14, 000-000. Walmsley A. D., Laird W. R. E. and Williams A. R. (1984) A model system to demonstrate the role ofcavitational activity in ultrasonic scaling. J. Dent. Res. 63, 1162-1165. Walmsley A. D., Laird W. R. E. and Williams A. R. (1986a) Displacement amplitude as a measure of the acoustic output of ultrasonic scalers. Dent. Mater. 2, 97-100. Walmsley A. D., Laird W. R. E. and Williams A. R. (1986b). Inherent variability of the performance of the ultrasonic descaler. J. Dent. 14, 121-125. Walsh T. F. and Waite I. M. (1978) A comparison of post-surgical healing following debridement by ultrasonic or hand instruments. J. Periodontol. 49, 201-205. Wells P. N. T. (1977) Biomedical Ultrasonics. Academic Pres, London. Williams A. R. (1983) Ultrasound: biological effects and potential hazards. Academic Press, London. Wilson J. R. (1958) The use of ultrasonics in periodontal treatment. J. Prosthet. Dent. 8, 161-166. Zinner D. D. (1955) Recent ultrasonic dental studies including periodontia, without the use of an abrasive. J. Dent. Res. 34, 748-749.