Bruce Matthews

Fluid flow through cat dentine in vivo

An outward flow of fluid through exposed dentine was demonstrated in anaesthetized cats. The flow was measured by observing the movement of the fat droplets of dilute milk in a glass capillary (i.d. 30 microns) with a microscope. The capillary was sealed to the dentine with a plastic cap. The resting flow rate through dentine exposed by fracturing off the tip of a cats canine ranged from 2.8 to 50.9 pl.s-1.mm-2 (mean 18.1, SD 15.9, n = 12). Raising the pressure at the dentine surface to about 15 cmH2O stopped the flow. Immediately after cutting the pulp at the root apex, in 11 of 12 preparations, the flow reversed. The average flow rate was then 3.8 pl.s-1.mm-2 inward (range 8.4 outward to 15.9 inward, SD 5.4, n = 12). The inward flow after pulp section suggests that an osmotic effect may contribute to the net pressure causing flow. The average hydraulic conductance of the exposed dentine was 1.6 x 10(-8) m.s-1.kPa-1 (range 0.5-2.9, SD 0.8) before pulp section. After pulp section, it increased to an average of 2.5 x 10(-8) m.s-1.kPa-1 (range 0.8-5.2, SD 1.3).

Interactions between neural and hydrodynamic mechanisms in dentine and pulp

Evidence is presented that the rate of inward diffusion of chemicals through exposed dentine is affected by the rate of outward flow of fluid through the dentinal tubules. Such a flow has been demonstrated in cats. The flow rate appears to depend upon the pulpal tissue-fluid pressure; flow increased during pulp vasodilatation and decreased, even reversing in direction, during vasoconstriction. Pulp vasodilatation can be produced by stimulating intradental afferent nerves, including some of those that seem to be excited by displacement of tubule contents (i.e. by a hydrodynamic mechanism). Thus, when dentine is exposed and these afferents are stimulated they will help to protect the pulp by producing reflex vasodilatation, which will decrease the rate of diffusion of toxins from the mouth into the pulp. The relation between the rate of flow through dentine and the discharge evoked in intradental nerves was investigated in cats. Single fibres were more sensitive to outward than to inward flow. The flow rates required to excite the pulp afferents were greater than those observed during even maximal pulpal vasodilatation.

Receptors involved in the response of the masseter muscle to tooth contact in man

Abstract Inhibition of the masseter muscle which follows mechanical stimulation of a tooth was not abolished by local anaesthesia of the tooth, indicating that receptors other than those in the periodontal tissue were involved. It was found that the inhibition was preceded by reflex activation of the muscle and this was attributed to stimulation of its spindles. A similar pattern of activity to that which followed tapping a single tooth was also found during chewing and during tooth-tapping in centric occlusion. The same response could also be obtained by eliciting a jaw-jerk or vibrating the skull while the subject was biting on a bung to produce a sustained contraction in the muscle. It is suggested that the inhibition was a consequence of the initial reflex contraction in the muscle.

CHANGES IN THE ACTIVITY OF THE MASSETER MUSCLE FOLLOWING TOOTH CONTACT IN MAN

Abstract Changes in the electrical activity of the masseter muscle immediately after tooth contact have been investigated in adult subjects who were instructed either to tap their teeth together in centric occlusion or to chew a cube of wax. Tooth contacts were monitored with a microphone taped to the forehead. In all the subjects tooth contact was followed by a period of reflex inhibition of masseter activity. The return of activity after this inhibition was variable and depended upon the voluntary efforts of the subject.

Experiments on extracted teeth into the validity of using laser Doppler techniques for recording pulpal blood flow

The performances of two laser Doppler flow meters (Periflux model PF3 and Moor Blood Flow Monitor model MBF3D) were investigated. Recordings were made while diluted blood was pumped at different rates through the pulp cavities of extracted human or pig teeth. The probe of each instrument was fixed to the enamel surface 2 mm from the original position of the gingival margin. Both instruments performed similarly, although the Moor gave the better signal/noise ratios. Both were capable of detecting flow in the core of the pulp as well as the superficial part closest to the probe tip. With either instrument, and with any one dilution of blood (range 0.5-45% v/v red cells), there was a near-linear relationship between the blood-flow signal and the flow rate of blood through the tooth. However, when data obtained with different red-cell concentrations were compared, a good correlation between the blood-flow signal and red-cell flux (product of concentration and mean velocity) was obtained only with red-cell concentrations up to 1% v/v. Therefore these instruments would give an accurate indication of blood flow changes only under conditions in which either this value was not exceeded or if the red-cell volume fraction remained constant; neither of which can be assumed to apply when recording from teeth in situ. The signals representing the concentration of moving blood cells were unreliable in both instruments. It is concluded that the information provided by these laser Doppler flow meters can be ambiguous and must be interpreted with care.

Osmotic stimulation of human dentine and the distribution of dental pain thresholds

Abstract It has been established that there is a relationship between osmotic pressure and pain-producing power when CaCl 2 solutions in the range 200–2800 atm are applied to dentine ( Anderson and Ronning , 1962). Experiments have been performed in an attempt to explain previous failure to confirm this relationship with other solutions. The experiments fell into two groups: those with solutions in the range 25–700 atm and those in the range 200–2800 atm. A decline in sensitivity during an experiment was observed as previously but was found to be caused only by solutions in the high range of osmotic pressure. Because of this decline in sensitivity, only the first results of every sequence of stimulations with the high range of osmotic pressures is comparable with results from the low range of osmotic pressures. Comparable data over the entire range of osmotic pressures 25–2800 atm was obtained by selecting only the first results of every series in the high range and using all the results in the low range of osmotic pressures. When this selection was made, the points on a graph of pain-producing power and log osmotic pressure fell on a sigmoid curve. This curve can be considered to represent the distribution of pain thresholds within the group of subjects, defined in units of log osmotic pressures. Probit transformation has shown that this distribution is normal (Gaussian). Osmotic pressure can therefore be taken as the effective stimulus common to all the solutions used in evoking pain from dentine.

The sources of laser Doppler blood-flow signals recorded from human teeth

Records of pulpal blood flow obtained from human teeth with a laser Doppler flowmeter include a very large component derived from periodontal and other tissues outside the pulp, but this contamination can be reduced by covering the surrounding tissues with opaque rubber dam. The present experiments were carried out to determine what proportion of the signal obtained with this dam in place is derived from non-pulpal tissues. Recordings were made from 22 healthy, intact upper incisors in 14 individuals (aged 22-40 years) with and without dam under the following conditions: from the intact teeth, after local anaesthesia (LA) and the preparation of a deep cavity in the incisal third of the labial surface of the tooth, and after removal of the pulp and arrest of bleeding. In some cases, a reading was also made after replacing the pulp in the pulp cavity. The rubber dam reduced significantly (P<0.05) the mean blood flow reading from the intact teeth by 73%, from 6.98 arbitrary perfusion units (PU) (+/-1.30 S.D., n=22) to 1.92+/-1.50 PU. After LA and cavity preparation, the mean signal with dam was 1.45+/-0.61 PU (n=16). This fell significantly by 76% to 0.35+/-0.19 PU (n=16) when the pulp was removed but not replaced, and by 43% to 0.98+/-0.36 PU (n=14) when the pulp was removed and replaced in the pulp cavity. The latter condition is thought to reproduce most closely the scattering of light in an intact tooth. The results confirm previous findings that up to 80% of the laser Doppler blood-flow signal recorded from an intact human tooth without rubber dam is of non-pulpal origin. They also show that only approximately 43% of the signal recorded with an opaque rubber dam is from pulp.

A computer-based method of measuring facial asymmetry. Results from an assessment of the repair of cleft lip deformities

The appearance of the nose, mouth and nostrils was analysed in two series of unilateral, complete cleft lip patients. A programme was written for use on a BBC microcomputer to measure the symmetry of facial features traced from photographs. Symmetry was measured using one of two methods: determining the area of non-overlap when one side was reflected on the other (area method) or calculating the distance from regularly spaced points on the outline of one side to the nearest point on the reflection of the opposite side (curve method). The rankings of the photographs based on these results were compared with the subjective rankings given by a lay panel. The results based on the curve method agreed well with the subjective rankings (P for Spearman Rank Correlation Coefficients = less than 0.02). The technique provides a cheap, simple and quick method of comparing symmetry in groups of patients.

A silent period in the masseter electromyogram following tooth contact in subjects wearing full dentures

Abstract A silent period in the masseter EMG has previously been observed following tooth contact in man. This has usually been attributed to inhibition of the muscle arising from stimulation of periodontal mechanoreceptors. Investigation of the masseter EMG of edentulous subjects wearing full dentures has shown that the changes in muscle activity that follow tooth contact are similar to those of subjects with natural teeth. These experiments provide evidence that the silent period does not necessarily depend upon stimulation of periodontal mechanoreceptors.

The permeability of human dentine in vitro and in vivo

Experiments in cats have shown that Evans blue dye diffuses at a greater rate into dentine in recently extracted teeth than in vivo. These experiments have now been repeated in man and similar results were obtained except that, after applications in vivo, visible concentrations of the dye were present in the dentine, and in a few cases, even in the pulp. It is concluded that, as in the cat, the diffusion in vivo was impaired by outward flow of fluid in the dentinal tubules but the mean velocity of flow in the human dentine was less than that in the cat.