Fluoride content of tank water in Australia

BACKGROUND

The aims of this study were to: (1) analyse the fluoride content of tank water; (2) determine whether the method of water collection or storage influenced fluoride content; and (3) survey participant attitudes towards water fluoridation.

METHODS

Plastic tubes and a questionnaire were distributed through dentists to households with water tanks in Victoria. A midstream tank water sample was collected and fluoride analysed in triplicate using ion chromatography

RESULTS

All samples (n = 123) contained negligible amounts of fluoride, with a mean fluoride concentration of <0.01 ppm (range: <0.01-0.18 ppm). No statistically significant association was found between fluoride content and variables investigated such as tank material, tank age, roof material and gutter material. Most people did not know whether their tank water contained fluoride and 40.8% preferred to have access to fluoridated water. The majority thought fluoride was safe and more than half of the respondents supported fluoridation. Fluoride content of tank water was well below the optimal levels for caries prevention.

CONCLUSIONS

People who rely solely on tank water for drinking may require additional exposure to fluoride for optimal caries prevention.

The microanatomy of the rhesus monkey temporomandibular joint

PURPOSE

The objective of this study was to describe and compare the histology of the rhesus monkey temporomandibular joint (TMJ) with that of the human joint.

MATERIALS AND METHODS

Seventeen rhesus monkeys (Macaca mulatta) with an age range from 4 to 11 years were used. Both TMJs of the first animal and the left TMJs of the remaining 16 animals were used for this study. The joint specimens were sectioned sagittally and processed for light and electron microscopic studies.

RESULTS

The rhesus monkey TMJ consists of the condylar, glenoid fossa, and articular disc components. The histology of these components is described at the light and electron microscopic level.

CONCLUSIONS

The monkey TMJ was found to be anatomically similar to the human joint. It was concluded that the rhesus monkey is one of the most suitable animal models for studies involving the TMJ.

A comparative study on meniscectomy and autogenous graft replacement of the rhesus monkey temporomandibular joint articular disc--Part II

This study investigated the effects of free auricular cartilage and pedicled temporalis myofascial flap replacement of the temporomandibular joint articular disc in eight rhesus monkeys (Macaca mulatta). The eight animals were divided into two groups (four animals in each group) for replacement of the disc with either auricular cartilage graft or pedicled temporalis myofascial graft. Degenerative changes (osteoarthritis) were observed in all the experimental joints. Despite degeneration of grafted cartilage tissue, histologic and clinical responses after auricular cartilage grafting were favourable. Pedicled temporalis myofascial flap resulted in re-formation of a disc-like interpositional structure in most of the studied joints with the most favourable histologic response.

A comparative study on meniscectomy and autogenous graft replacement of the Rhesus monkey temporomandibular joint articular disc--Part I

The aims of this study were to compare the effects of meniscectomy and autogenous graft replacement on the functions and histology of the Rhesus monkey temporomandibular joint. Eight matured Rhesus monkeys (Macaca mulatta) were used for the first part of the study to compare firstly the results of meniscectomy without replacement and secondly, replacement of the disc with a fascia lata graft. The results showed that unilateral meniscectomy in Rhesus monkeys did not result in significant morbidity. Degenerative changes (osteoarthritis) were observed in all the experimental joints with and without replacement of the articular discs. Fascia lata did not survive after grafting and did not reliably induce re-formation of an articular disc-like structure.

Incidence of complicated healing and osteoradionecrosis following tooth extraction in patients receiving radiotherapy for treatment of nasopharyngeal carcinoma

A group of 43 patients requiring tooth extraction after radiotherapy for nasopharyngeal carcinoma (NPC) was studied retrospectively to determine the incidence of post-extraction complications. It was found that because of the method used in the delivery of radiation, extraction of maxillary posterior teeth resulted in the greatest risk of complications (28.9 per cent), including a 10.5 per cent risk of osteoradionecrosis (ORN). Based on the findings, a protocol was established for the dental care of such patients. It was concluded that when extraction of maxillary posterior teeth was necessary, prophylactic antibiotics were not sufficient to prevent the complication of delayed healing. The risk of ORN was 10.5 per cent within the field of maximal radiation dose. Hyperbaric oxygen may be the better choice of preventive measures. However, in view of the low risk of ORN, wholesale prescription of hyperbaric oxygen therapy may not be indicated. An additional patient who had tooth extraction two weeks prior to radiotherapy was included to show that if adequate time for wound healing was not allowed, ORN could develop.

Increased metabolism of infused 1-methylxanthine by working muscle

Exogenous substrates for capillary endothelial enzymes have potential as markers for changes in capillary recruitment (albeit nutritive flow). The metabolism of infused 1-methylxanthine (1-MX) to 1-methylurate (1-MU) by capillary endothelial xanthine oxidase of the constant-flow perfused rat hindlimb was shown previously to decrease with oxygen uptake (VO2) when nutritive flow was decreased. In the present study, the metabolism of 1-MX was investigated under conditions when VO2 and nutritive flow are known to increase during muscle contraction. The constant-flow red blood cell-perfused rat hindlimb at 37 degrees C was used with sciatic nerve stimulation, and perfusate samples from whole hindlimb and working muscles taken for analysis of oxygen, lactate, 1-MX and 1-MU. Flow to muscle was assessed separately using fluorescent microspheres and was found to increase 2.3-fold to the working muscles while flow to the non-working leg muscles decreased to compensate. The activity of xanthine oxidase of whole muscle extracts was not altered by contraction. Samples from the vein draining the working muscles, and microsphere measurements of flow, indicated increased VO2 (5.5-fold to 249.2 +/- 43.1 micromol h-1 g-1, P < 0.001), and 1-MX conversion (2.5-fold to 1.87 +/- 0.25 micromol h-1 g-1, P < 0.01) (SEM are shown). It is concluded that as 1-MX metabolism parallels VO2, this substrate may be a useful indicator of changes in capillary (nutritive) surface area in muscle.

Na+ channel and Na+-K+ ATPase involvement in norepinephrine- and veratridine-stimulated metabolism in perfused rat hind limb

In the constant flow perfused rat hind limb, norepinephrine (NE) evoked increases in oxygen uptake (VO2) and lactate efflux (LE) were inhibited by the cardiac glycoside ouabain (1 mM), without interrupting the NE-mediated vasoconstriction. The membrane labilizer veratridine, previously shown to increase VO2 and LE, without increasing perfusion pressure, was also shown to be inhibited by the cardiac glycoside ouabain, as well as by the ouabain analogues digitoxin and digoxin. The stimulatory actions of veratridine on VO2 were inhibitable by low doses of the specific sodium channel blocker tetrodotoxin (TTX), while NE effects were unaffected, suggesting that NE may be acting via a TTX-insensitive sodium channel. It is concluded that agents such as NE (a vasoconstrictor) or veratridine (a membrane labilizer), which stimulate VO2 in the perfused rat hind limb, do so by increasing Na+ influx. The observed increases in oxygen consumption and LE are due to Na+-K+ ATPase activity to pump Na+ out of the cell at the expense of ATP turnover. Energy dissipation due to Na+ cycling may be a form of facultative thermogenesis attributable to NE that can be stimulated by membrane labilizers such as veratridine in the constant flow perfused rat hind limb.

Similarities between vasoconstrictor- and veratridine-stimulated metabolism in perfused rat hind limb

The vasoconstrictors norepinephrine (NE) and angiotensin II (AII) mediate increases in oxygen uptake (VO2) by the constant flow perfused rat hind limb that are inhibited by quinidine-like membrane-stabilizing effects (involving the interruption of action potential) of (+/-)-propranolol with little effect on vasoconstriction. The membrane labilizer veratridine, 10 microM, which has the capability of maintaining voltage-gated Na+ channels of the plasma membrane in their open state, also increases VO2 but without an increase in pressure. Thus in the present study veratridine was characterized in detail and compared with NE in the same system. Veratridine (3-100 microM) produced a dose-dependent stimulation of VO2 (from 11.8 +/- 0.3 to 20.4 +/- 0.6 mumol.h-1.g-1 (n = 5), p < 0.0001) and lactate efflux (LE) (from 7.4 +/- 0.6 to 23.0 +/- 4.7 mumol.h-1.g-1 (n = 5), p < 0.01). These increases were independent of vasoconstriction at low doses (< or = 10 microM). At higher doses of veratridine the accompanying minor vasoconstriction (from 17 +/- 1 to 30 +/- 2 mmHg (1 mmHg = 133.3 Pa) (n = 5), p < 0.005) was blocked by sodium nitroprusside (NP) while neither VO2 nor LE was greatly affected. Low Na+ perfusions (25 mM) did not affect the vasoconstrictor action of NE but markedly inhibited increases in VO2 and LE due to either veratridine or NE. Veratridine (10 microM) mediated increases in VO2 and LE were blocked by either (+/-)-propranolol (100 microM) or 150 microM quinidine. It is concluded that vasoconstrictors such as NE, which stimulate VO2 in the perfused rat hind limb, do so by a two-stage process involving an essential nitroprusside-sensitive redirection of flow followed by a mechanism involving increased ion movement across skeletal muscle cell membranes, which is blocked by membrane stabilizers. Veratridine achieves a similar increase in VO2 but may do so by directly destabilizing the skeletal muscle cell membrane without the requirement of a redirection of flow.

Vasoconstrictor-mediated increase in muscle resting thermogenesis is inhibited by membrane-stabilizing agents

Norepinephrine and angiotensin II are potent vasoconstrictors and stimulate thermogenesis (oxygen uptake) as well as lactate and glycerol efflux in the constant-flow perfused rat hind limb at rest. However, the mechanism by which oxygen uptake (VO2) is increased is unknown, and it is not clear whether vasoconstriction is required for the increase in VO2 by the hind limb. In the present study the association between vasoconstriction and VO2 was further investigated, and a chance observation that high-dose propranolol selectively blocked vasoconstrictor-induced increase in VO2 was further explored. The norepinephrine-mediated increase in VO2 was totally blocked by either 50 microM (+)-propranolol or 50 microM (-)-propranolol (active beta-blocking enantiomer), but only (+)-propranolol reduced the vasoconstriction. Similarly, 100 microM (+/-)-propranolol (a dose likely to cause plasma membrane stabilizing effects involving interruption and (or) prevention of action potentials) blocked increases in VO2, lactate, and glycerol efflux by 5 nM angiotensin II (a nonadrenergic vasoconstrictor) with only marginal effects on pressure development. (+/-)-Propranolol (100 microM) had no effect on postequilibration red blood cell washout mediated by angiotensin II, a putative indicator of vasoconstrictor-induced redistribution of flow. Quinidine (260 microM) (an antiarrhythmic agent with membrane-stabilizing activity) inhibited only the increase in VO2, but neither nadolol (300 microM) nor atenolol (300 microM) (beta-blockers without membrane-stabilizing activity) inhibited VO2 or perfusion pressure increases produced by 5 nM angiotensin II. Veratridine (a membrane labilizer that is capable of evoking plasma membrane depolarization by maintaining voltage-gated Na+ channels in their open state) increased VO2 without vasoconstriction, and the increase in VO2 was blocked by 100 microM (+/-)-propranolol. It is concluded that the increase in hind-limb VO2 results from a destabilization of skeletal muscle plasma membranes. This can be achieved directly by veratridine or indirectly by angiotensin II, involving vasoconstriction and redistribution of flow. The findings suggest a novel mechanism for resting muscle thermogenesis.

Perfused skeletal muscle contraction and metabolism improved by angiotensin II-mediated vasoconstriction

In the present study, the effects of angiotensin II (ANG II) on tension development and associated metabolism during twitch and tetanic stimulation via the sciatic nerve of the gastrocnemius-plantaris-soleus muscle group of the perfused rat hindlimb were investigated. Rat hindlimbs were perfused at constant flow with an erythrocyte-containing medium equilibrated with 95% air-5% CO2 at 37 degrees C, and determinations of oxygen and glucose uptake, lactate and glycerol release, and 2-deoxy-D-[1-3H]glucose uptake (Rg') into individual muscles were carried out. ANG II (1 nM) infusion alone caused vasoconstriction with increased oxygen (55%) and glucose (98%) uptake and lactate (37%) and glycerol (64%) release. ANG II infusion during muscle contraction gave less vasoconstriction but increased the tension development during tetanic stimulation by 80% and increased the contraction-induced oxygen uptake and Rg' by plantaris and gastrocnemius red and white muscles. These effects of ANG II may have been due to increased nutritive flow to contracting muscles or to redirection of flow from noncontracting and type I fiber muscles to the type II fiber contracting muscles in the hindlimb. The results indicate that the regulation of flow by the vasculature is an important regulator of muscle contraction and metabolism.

Dental hygienists in Hong Kong: present and future status

PURPOSE

This study assessed the current employment status of dental hygienists practicing in Hong Kong, investigated factors affecting their employment, evaluated the satisfaction of local dental hygienists and their employers, and explored the career prospects of dental hygienists in Hong Kong.

METHODS

All registered dental hygienists (n = 64), all dentists who employed dental hygienists (n = 25), and a systematic sample of dentists who did not employ dental hygienists (n = 278) were surveyed in June 1994 concerning employment situation, salaries, job satisfaction, and opinions on future prospects for dental hygienists.

RESULTS

Response rates were 86% for dental hygienists (n = 55), 88% for employers (n = 22), and 63% for dentists at large (n = 175). Among the dental hygienists, 87% still were employed as dental hygienists, and both the dental hygienists and their employers agreed that the employment situation was satisfactory; however, several dental hygienists were considered to be working below their level of qualification. Major reasons for dentists not to employ a dental hygienist were having only one operatory and having an inadequate number of patients. In general, employers expressed satisfaction with the performance of the dental hygienists. Major reasons for employing a dental hygienist were that a dental hygienist would add professional and economical benefit to their clinic. Few dentists would support expanded duties for dental hygienists.

CONCLUSIONS

In Hong Kong, dental hygienists and their employers comprise a small group with limited impact on oral healthcare services. Dental hygienists' perceptions of their future roles and ambitions are higher than those of their employers. To further the development of dental services in Hong Kong and meet documented oral healthcare needs in the population, greater utilization of dental hygienists should be promoted.

Blood loss and transfusion requirements in orthognatic surgery

PURPOSE

This study quantified the blood loss and transfusion requirements in orthognathic surgery.

PATIENTS AND METHODS

Three hundred sixty consecutive healthy orthognathic surgery patients were included in this retrospective study. The female:male ratio was 1.8:1, and the age range was 8 to 49 years (mean, 24). Estimated blood volume (EBV), estimated blood loss (EBL), and transfused blood were calculated.

RESULTS

EBL ranged from 50 to 5,000 mL (mean, 600) representing up to 73% of EBV (mean, 16%). In total, 24% (84 patients) were transfused, 8.7% (6 patients) after single-jaw surgery and iliac bone harvest and 26.7% (78 patients) after bimaxillary osteotomies. Forty-seven patients received 1 unit of transfused blood, 25 patients had 2 units, and 12 patients had more than 2 units. Most transfused patients lost 11% to 40% of EBV.

CONCLUSIONS

Transfusion is not necessary for single-jaw surgery unless a bicoronal flap or iliac bone harvest are required. Although only 27% of bimaxillary osteotomy patients required transfusion of 1 to 2 units, this group was not predictable based on the type of procedure involved, and a further subgroup (4% of the 291 patients) required a larger transfusion.

Mandibular reconstruction with the Dacron urethane tray: a radiologic assessment of bone remodeling

A retrospective study was made of 22 consecutive patients who underwent mandibular reconstruction with a Dacron (Osteo-mesh, Xomed Inc, Jacksonville, FL) tray technique from September 1988 to April 1992. Free autogenous iliac bone, in the form of particulate cancellous chips and marrow, was densely packed into the Dacron tray, that was adapted to bridge the mandibular segmental defect. Sixteen cases underwent uneventful healing with the formation of a continuous bony bridge and union with the remaining mandible. The pattern of bone remodeling and rate of resorption in these cases were assessed by sequential panoramic radiographs taken up to 3 years postoperatively. The mean horizontal dimension of the mandibular defects was 75 mm and the mean vertical reconstructed height was 25 mm. When the grafted bone was radiographically of uniform density, it progressed into a mature trabecular pattern matching that of the normal mandible. However, when there were areas of radiolucency, most likely from inadequate condensation of the graft, such areas were not replaced by bone in the long term. The bony height at both ends and the middle of the reconstructed segment underwent reasonably even resorption and retained about 80% of the bony height over a 3-year period. The rate of resorption was highest in the first 6 months and stabilized at about 2 years. There were six failures, all showing significant irregular bony resorption prior to tray removal.