Abfraction: separating fact from fiction.

Non-carious cervical lesions involve loss of hard tissue and, in some instances, restorative material at the cervical third of the crown and subjacent root surface, through processes unrelated to caries. These non-carious processes may include abrasion, corrosion and possibly abfraction, acting alone or in combination. Abfraction is thought to take place when excessive cyclic, non-axial tooth loading leads to cusp flexure and stress concentration in the vulnerable cervical region of teeth. Such stress is then believed to directly or indirectly contribute to the loss of cervical tooth substance. This article critically reviews the literature for and against the concept of abfraction. Although there is theoretical evidence in support of abfraction, predominantly from finite element analysis studies, caution is advised when interpreting results of these studies because of their limitations. In fact, there is only a small amount of experimental evidence for abfraction. Clinical studies have shown associations between abfraction lesions, bruxism and occlusal factors, such as premature contacts and wear facets, but these investigations do not confirm causal relationships. Importantly, abfraction lesions have not been reported in pre-contemporary populations. It is important that oral health professionals understand that abfraction is still a theoretical concept, as it is not backed up by appropriate clinical evidence. It is recommended that destructive, irreversible treatments aimed at treating so-called abfraction lesions, such as occlusal adjustment, be avoided.

Self-perceived competency at graduation: a comparison of dental graduates from the Adelaide PBL curriculum and the Toronto traditional curriculum.

The first class to complete the new Adelaide problem-based learning curriculum graduated in 1997. Their self-perceived competence at graduation was assessed using a revised version of a questionnaire recently compiled and used in Toronto, and based on the global competencies for dental practice accepted in 1995 by all Canadian Faculties of Dentistry. 38 of the 45 Adelaide class members (84%) completed the survey, compared with 93/129 (72%) in Toronto, and their responses were largely similar to those of the Toronto students. At least 67% of the Adelaide and Toronto students felt well-prepared in 34 of the 55 competencies. Most felt well-prepared for the basic everyday items such as diagnosis, local anaesthesia and basic restorative, but less so for items that are not encountered as often in dental school, such as business matters, practice management, soft tissue biopsies and dentofacial trauma. Items showing significant differences between the 2 schools are discussed with reference to curricular and other dissimilarities in the schools, and some inferences are drawn about the importance of context to learning and feelings of competence.

How competent do our graduates feel?

As part of a review of the undergraduate curriculum to assess its relevance for a future general practitioner, a survey of self-perceived competency at graduation based on the competency list developed by the Association of Canadian Faculties of Dentistry was circulated to recent graduates and the graduating class. The overall response was 67.5 percent, and revealed that approximately 70 percent of the respondents felt well prepared in approximately 69 percent of the competencies. These were the common "bread and butter" items of dentistry, such as basic restorative dentistry, examination, diagnosis, treatment planning, local anaesthesia, and scaling. Those areas reported as less well-prepared for included financial and personnel management, performance of soft-tissue biopsies, and management of chronic orofacial pain. Clarification of the raw survey results in focus groups was needed to uncover specific details that could lead to remedial action in problem areas.

Inputs to trigeminal brain stem neurones from facial, oral, tooth pulp and pharyngolaryngeal tissues: II. Role of trigeminal nucleus caudalis in modulating responses to innocuous and noxious stimuli.

Trigeminal (V) tractotomy and cold block of synaptic transmission in V nucleus caudalis were used to show that caudalis modulates the responses to innocuous and noxious stimuli of single V main sensory-oralis neurones recorded in anaesthetized or decerebrate cats. Cold block caused a reversible depression of mechanosensitivity of 91 of 105 V-thalamic relay and non-relay cells tested; V tractotomy also decreased sensitivity. The possibliity that the effects observed with cold block of caudalis were caused by direct spread of cooling to the main sensory-oralis region, and not by depression of a tonic, net facilitatory influence of caudalis on main sensory-oralis cells, was ruled out by several controls. With cold block of caudalis there also occurred a reversible shrinkage in mechanoreceptive field size and reversible reduction in sensitivity of rapidly adapting and slowly adapting mechanoreceptive neurones. Occasionally no change or an increase in sensitivity occurred, the latter suggesting the liklihood of an inhibitory influence from caudalis as well as the facilitatory influence. The effects of interactions of innocuous and noxious V stimuli were likewise subject to ascending influences from caudalis. Cold block also reversibly depressed responses to tooth pulp and V cutaneous noxious stimuli, although pulp-evoked responses were depressed less than mechanical or infraorbital nerve-elicited responses. Our results indicate that caudalis, as well as acting as a relay site to thalamus, also exerts a predominantly facilitatory influence on the relay to the thalamus and local reflex centres of mechanoreceptive and nociceptive information through the V main sensory-oralis region. The findings also might in part explain the analgesia, partial loss of tactile sensibility, and relief from V neuralgia reported after V tractotomy.

Inputs to trigeminal brain stem neurones from facial, oral, tooth pulp and pharyngolaryngeal tissues: I. Responses to innocuous and noxious stimuli.

Responses evoked in anaesthetized or decerebrate cats by stimulation of afferents supplying the face, mouth, pharynx, larynx, tooth pulp and jaw muscles were recorded from single neurones located in the trigeminal (V) main sensory nucleus, V nucleus oralis, and adjacent regions. Many cells (both V-thalamic relay and non-relay with localized V mechanoreceptive cutaneous fields could be activated by stimulation of a number of these afferents. A particularly prominent short-latency (often monosynaptic) input was noted from the canine tooth pulp, stimulation of which is generally considered to elicit only responses of pain in man. Control experiments showed that pulp-evoked responses were not the result of stimulus spread to tissues outside the pulp. The interaction of these various inputs to neurones at this level of the V brain stem complex typically resulted in a prolonged period of inhibition that was sometimes preceded by a short-lasting facilitatory phase. This inhibitory effect was also apparent in neurones located outside the complex, although a late facilitatory phase was frequently also noted. Our findings indicate a significant nociceptive input to V main sensory-oralis neurones, a proportion of which relay directly to the ventrobasal thalamus. The interactions described may be involved in perceptual and reflex aspects of responses to noxious and innocuous V stimuli.

Descending influences of periaqueductal gray matter and somatosensory cerebral cortex on neurones in trigeminal brain stem nuclei.

Single relay (to thalamus) and nonrelay neurones that responded to innocuous and/or noxious oral-facial stimuli were located in trigeminal brain stem nuclei oralis and caudalis. The responses of the cells and the digastric muscle to these stimuli were tested with conditioning stimulation of the periaqueductal gray matter (PGM) and somatosensory cerebral cortex in cats. A greater suppression of nociceptive responses with PGM stimulation was noted, and this effect may contribute to the profound analgesic action that has been reported to occur with PGM stimulation.

The slowing of gastric emptying by monosaccharides and disaccharides in test meals.

1. Test meals containing various concentrations of glucose, maltose, sucrose, fructose, lactose, galactose and mixtures of these solutes were given to six healthy subjects. All meals contained 40 mM sodium citrate.2. The slowing of gastric emptying produced by the disaccharides in test meals was generally consistent with the stimulation of duodenal osmoreceptors occuring after the hydrolysis of the disaccharides.3. Glucose was slightly more effective, per osmole, in slowing gastric emptying than was galactose.4. By comparison with glucose or galactose, fructose was much less effective in slowing gastric emptying. In three subjects out of six there was a threshold for its effect.5. The results may be indicative of the relative activities of disaccharidases in the brush border of the small intestine. They are consistent with there being an osmoreceptor deep to these enzymes which slows gastric emptying.