The use of laser Doppler flowmetry in paediatric dentistry.
Abstract: BACKGROUND: An early determination of pulpal vitality is crucial with respect to a correct differential diagnosis of revascularisation or necrosis and its treatment. REVIEW: Sensibility tests (cold, heat, electrical pulp test) in combination with radiographs are commonly promoted. However these tests are arbitrary, based on sensations and therefore not always reliable. In such situations registration of pulpal blood flow will be advantageous. The most studied and well documented method for registration of blood circulation is laser Doppler flowmetry (LDF) which is typified as a non-invasive technique with direct and objective registrations. In this article blood flow, LDF and its characteristics, the advantages and disadvantages of the methods and the latest developments regarding LDF is described. CONCLUSION: Despite there being a low implementation of LDF in dentistry to date, this should become one of the basic techniques for clinical use in paediatric dentistry.

Key words: Revascularisation, laser Doppler flowmetry, vitality and sensibility tests, pulpal blood flow.
Article Type: Report
Subject: Doppler ultrasonography (Usage)
Doppler ultrasonography (Health aspects)
Lasers in medicine (Usage)
Pedodontics (Analysis)
Authors: Roeykens, H.
De Moor, R.
Pub Date: 04/01/2011
Publication: Name: European Archives of Paediatric Dentistry Publisher: European Academy of Paediatric Dentistry Audience: Academic Format: Magazine/Journal Subject: Health Copyright: COPYRIGHT 2011 European Academy of Paediatric Dentistry ISSN: 1818-6300
Issue: Date: April, 2011 Source Volume: 12 Source Issue: 2
Product: Product Code: 3832848 Lasers for Medicine NAICS Code: 334510 Electromedical and Electrotherapeutic Apparatus Manufacturing SIC Code: 3845 Electromedical equipment
Geographic: Geographic Scope: Belgium Geographic Code: 4EUBL Belgium
Accession Number: 277106747
Full Text: Introduction

There are several ways in which the presence of blood in tissue can be measured. This can be performed firstly with the use of light such as photoplethysmography (FPG) (pulsoxymeter) [Diaz-Arnold et al., 1994; Jafarzadeh and Rosenberg, 2009] or laser Doppler flowmetry (LDF) but also secondly by injecting radioactive particles followed by medical imaging i.e. the 133Xenon washout method [Kim et al., 1990] or thirdly by echo Doppler ultrasound. When LDF registers the blood perfusion, photoplethysmography will monitor blood volume changes.

Blood micro-circulation is very specific for teeth. Taking into account the environment where capillaries are located, the microspheres and washout but also the ultrasound techniques will not be used as absolute calibrations as they are not direct and non-invasive. The preference therefore is for LDF especially because of its simple, cheap, and accessible technology. The latter also surpasses FGP due to an enhanced specificity and sensitivity for micro-capillary tubes [Kim et al., 2008]. LDF was originally developed to measure the blood flow of micro-vascular systems such as the retina [Riva et al., 1972], cortex of the kidney [Stern, 1975] and skin tissue [Holloway and Watkins, 1977]. Gazelius et al. [1986] demonstrated the usefulness of LDF in dentistry as a noninvasive, objective, continuous technique with the possibility of recording and analysing blood flow in teeth. It is only lately that publications concerning multiple technologies followed with a number of very specific applications, such as the use in dental traumatology [Roeykens et al., 2002], periodontology [Patino-Marin et al., 2005] and orthodontic surgery [Emshoff et al., 2000]. Since the initiation of LDF in dentistry there have been 266 publications to date (search term: laser Doppler and dentistry).

Working mechanisms. Light from a near infrared diode laser is passed through a metal probe with an optical fibre onto the surface of a tissue. When tooth and pulpal tissue are involved, enamel prisms and dentine tubules will lead the laser beam to the pulpal capillaries where the light is diffused by fixed and static tissue as well as by moving red blood cells. Red blood cells are the largest moving cells within blood.

According to the Doppler principle, the moving red blood cell backscattered light rays are subjected to a frequency shift where this is not the case for static tissue. The 'mix' of frequency shifted and un-shifted light goes back to the surface of the tooth (tissue), where it is absorbed by an optical glass fibre in the same probe connected to photo detectors. This frequency shift is called a Doppler shift. It is important to mention that the particles conveyed by a fluid flow to be measured must be big enough to scatter sufficient light for signal detection but small enough to follow the flow faithfully [Jafarzadeh, 2009]. The difference of the incoming and outgoing light frequencies is an electric potential (mV) that is in proportion to the average rate at which the (red) blood cells are moving (blood speed) with the product of the concentration. This is called the flux or blood perfusion.

The frequency difference (Doppler shift amount) of these two light components is detected on the surface of a photo detector by a phenomenon called optical beating (when two waves mix, the resulting sum of waveforms has a 'beat frequency' that is equal to the difference between the two original wave frequencies). The resulting photocurrent undergoes analogue and digital signal processing (DSP) to produce flux and concentration parameters related to the movement and concentration of the blood cells. The difference between the flux and the concentration is proportional to the integral of the full power spectrum without the weighting (w). In the interpretation of these data, the Doppler shifted frequencies will be extrapolated from the background noise (noise frequency = irregular scattered laser light) and other interference frequencies.

Arbitrary units. LDF outcomes are expressed in arbitrary units (AU) as a result of a non-linearity of the potential between the outbound light and the blood flow for all volume fractions of various red blood cells greater than 1% [linearisation alogarithm of Bonner and Nossal, [1981]. If an outgoing signal increases by 100%, the assumption cannot be made that the blood flow will also increase by 100%. A second reason for the use of AU is the absence of an absolute medium of calibration. The current clinical active calibration happens in an aqueous solution of polystyrene microspheres with a Brownian motion and is called 'motility standard'. A biological zero is not zero but an 'every time' calibration background reading. Moreover, as part of the LDF signal for a dental measurement is of non-pulpal origin, multiple factors will have a significant impact on the LDF readings. So we consider optical properties of the surrounding dentine and enamel (tooth discolouration), as well as the blood circulation of the surrounding gingival tissue and every movement of the patient or the probe but also stress the use of medications.

Materials and methods

For dental purposes, a He-Ne (632.8 nm) or a Diode (7808-10nm) laser has been used. The Diode laser scored slightly better in specificity and sensitivity [Ramsay et al., 1991; Hartmann et al., 1996]. The power of the device was at least 1.0 mW with 0.5 to 1.5 mW (diameter = 1.5mm) at the end of the probe. For measurements of tooth vitality a 3kHz bandwidth (broad-spectrum--low blood volume) and for measurements at the gingivoe a 14.3 kHz bandwidth was proposed. Values were recorded every 0.1 seconds but shown with a frequency of 40Hz over a minimum interval of 2 times 30 sec [Sooampon et al., 2003]. Afterwards, these data were processed in a spreadsheet (Excel, Microsoft Corp) and statistically analysed (SPSS / PC + statistical package, SPSS Inc.). For each patient a non-light permeable splint was made, after an acclimatisation period ([+ or -] 10 mins) in order to hold the probe.

The location of the probe was determined and a small hole was made in the splint, which was placed in the mouth, followed by insertion of the probe which stood perpendicular to the tooth surface. Each measurement took at least 30 secs in order to diagnose vasomotor changes, and was repeated twice. If possible, a contra-lateral tooth was simultaneously monitored [Mesaros et al., 1997; Roeykens et al., 1999]. To keep additional pulpal components in the readings as low as possible, a rigorous protocol had to be followed. Each patient was seated in a semi-supine position in a dental chair and using the same ambient light for each assessment. The best diagnostic results were obtained with drug-free and relaxed patients with clear medical histories. The use of a silicone resin or light-blocking holder, possibly in combination with a rubber dam and at least 2 x 30 secs measurement times for each recording is highly recommended but is time consuming.

LDF: a benefit? LDF is more reliable as compared to pulseoximetry and electric pulp test [Karayilmaz and Kirzioglu, 2010] or to classic 'sensitivity testing'. LDF scores 1.0 for sensitivity and 1.0 for specificity regarding vital or non-vital pulp tissue, a cold test with ethyl chloride scores 0.92 and 0.89 respectively, whereas this is 0.87 and 0.96 respectively with an electric pulp test. Both cold and electric pulp test were found missing 8-13% in sensitivity and between 4 and 13% in specificity [Evans et al., 1999]. The evaluation of heat versus cold and electric tests as a means of measurement of pulp vitality, gave 89% negative findings for pulp necrosis with the cold test, 48% with the heat test and 88% with the electric pulp test. For a 'vital pulp' a positive response was given respectively in 90% of all cases with cold, 83% with heat and 84% with electric pulp tests [Petersson et al., 1999]. For the case of LDF this was 100% in both situations. In addition, LDF can be used immediately after trauma where normal sensitivity tests will only provide 'reliable' information at the very best 6 weeks after a traumatic insult. Moreover the use of LDF in orthodontic surgery proved that a tooth without normal innervation may have an intact blood supply despite a negative response to other techniques [Kolkman, 1998]. LDF also highlighted a similar pattern of wound healing between a non-induced trauma (e.g. luxation) [Roeykens et al., 2002] and an induced trauma (Le Fort I osteotomy) [Justus et al., 2001]. LDF is therefore a technique that allows the practitioner to establish an early reliable diagnosis followed by the adequate treatment option [Roeykens et al., 2002; Patino-Marin et al., 2005; Emshoff et al., 2000].

Case reports

Case 1. Auto-transplantation of wisdom teeth and luxation of an auto-transplanted second upper premolar. In a 17-year-old Caucasian girl with congenital aplasia of 4 second premolars, both wisdom teeth were auto-transplanted to selected premolar sites in the mandible after orthodontic consultation. These transplants were performed at half-root formation stage with a follow-up period of 4 months to 4 years. The conditions, e.g. stage of root development and apical diameter were good on a radiograph at 2 months (Fig. 1a) before transplantation. A good integration of both wisdom teeth was shown both on radiograph and LDF showed vitality at 1 (Fig. 1b) and 4 years (Fig. 1c) after transplantation. Endodontic treatment was avoided. According to the method described by Roeykens et al. [1999], LDF evaluation was performed using a DRT 4 LDF monitor (Moor Instruments Ltd, Axminster, Devon, England Fig. 2) with a laser diode at 780nm and a probe output of 1.0mW was used. The manufacturer perscribed an output between 0.1 and 0.5 mW for zero flow conditions. The DRT 4 recorded tooth signals at a bandwidth of 3kHz with a time output constant of 0.1s. The display rate was set on 40Hz with a time span of 65s. Each probe ([empty set] = 1.5mm, optical fibres distance = 0.2mm and a 0.5mm separation of centres) was labelled and calibrated according to the manufacturer's instructions. A LDF signal was simultaneously obtained from both comparable teeth using two identical probes (Fig. 3).

Auto-transplantation of teeth is generally accepted as a reliable procedure in cases such as trauma [Kristerson and Lagerstrom, 1991], early loss and congenital aplasia, and concerns mainly youngsters [Andreasen, 1991]. The vitality of these elements is almost always diagnosed by means of sensitivity tests and verified with radiographs. According to Andreasen and Andreasen [2007] the five year survival for teeth with open apices and 2/3 root formation at the time of auto-transplantation is 98% and for ten years survival is at least 80%, but complications such as primary or secondary pulp necrosis occur in 10% and root resorption in 10-20% of cases.

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Case 2. A luxation of an auto-transplanted second maxillary premolar in an 13 year-old Caucasian girl was treated by transplantation of a first premolar into the alveolus of a maxillary central incisor. This transplantation was performed as the result of a previously unsuccessful re-plantation of the avulsed incisor that was luxated at the age of 11 years. This premolar transplantation was splinted for 10 days after trauma and followed for 6 months with a review after 4 years.

Once again a similar pattern of sensitivity values was obtained. After this severe trauma tooth vitality was preserved and was monitored by LDF (Fig. 4). Although a pattern of hyperaemia, ischaemia and restored vitality was observed, the differences over a period of 3 years were limited (Fig. 5).

Discussion

LDF is an objective, non-invasive and instantly readable recording method for blood flow from teeth with vascularisation problems. This technique can reduce the use of subjective and unreliable sensibility tests to a minimum. An early and accurate assessment of blood flow will be a significant asset to any treatment certainly given that the impact of trauma on the survival of the pulp usually starts at the time of the accident.

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Endodontic treatment based on inaccurate clinical information or the absence of an apical radiolucency can thus be avoided. In this particular case we found, as described by Andreasen and Andreasen [2007] where a high pulp survival rate was observed for teeth with closed root apices involved in alveolar bone fractures, endodontic treatment was not required even four years later.

An assessment with simultaneous recordings using two measuring probes has been proposed by Mesaros et al. [1997]. They followed a total avulsion and re-implantation of immature permanent upper incisors. Here the use of C[O.sub.2]-ice was compared with LDF. LDF proved to be the most effective and early indicator (3 weeks) for revascularisation of the pulp. In the present report this observation is confirmed and extended to an electric pulp test where reproducible values were obtained for both starting at week 7.

These long-term studies also show an evolution of hyperaemia followed by ischaemia and recovering vitality starting at week 9 (Fig. 5--transplant cases). These findings open a new insight into the role of treatment planning for similar trauma and treatments.

Conclusion

The value of LDF in dentistry today lies in the predictability of the treatment. Early recognition of a pulpal problem benefits the ultimate treatment and prognosis of a tooth. The simultaneous use of two measurement probes allows two adjacent or contra-lateral teeth to be instantly compared. Moreover, this objective technique convinces in both the short and long term as shown by the evolution of 'disturbed' to 'restored pulp perfusion or vitality' as demonstrated in the presented case reports. This will also account for the evaluation of blood flow for non-pulp related issues such as the need for re-vascularisation in tissue grafts, bone osteomyelitis and bone quality in monitoring the condition of the tissues surrounding implants. Despite the limited implementation of LDF in dentistry this technique belongs to the basic instruments of a dental clinic/ hospital. One should also keep in mind that there is a learning curve and costs associated with this new method.

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H. Roeykens, R. De Moor

Dept. of Operative Dentistry and Endodontology, School of Dentistry, University of Gent, Gent, Belgium.

Postal address: Dr. H. Roeykens, Dept. Restorative Dentistry and Endodontology, University of Ghent, De Pintelaan 185, 9000 Ghent, Belgium.

Email: Herman.Roeykens@ugent.be
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