Biomedical subjects

L C Richards

Publications and source records attributed to L C Richards.

At least 19 recordsLinked to original sources

PubMed2003

Tooth wear prevention: a quantitative and qualitative in vitro study.

BACKGROUND: Management of tooth wear from grinding presents a significant clinical challenge. Acrylic nightguards are often used to protect the teeth, but many patients still grind with these appliances. This study aimed to test the effectiveness of three lubricants in reducing enamel wear by using an electro-mechanical machine under controlled conditions, with a view to undertaking a subsequent longitudinal clinical study. METHODS: Sectioned tooth specimens were worn against each other under different loads and with the addition of three different lubricants: calcium fluoride (CaF) powder, olive-oil, and a combination of calcium fluoride with olive-oil in the form of a slurry. Wear rates of enamel only were quantified by weighing the specimens, and resin replicas of the worn tooth surfaces were made for examination under a scanning electron microscope. RESULTS: All three lubricants reduced the amount of enamel wear significantly compared with wearing specimens without adding lubricants. Wear rate was influenced by the type of lubricant and the load applied. Wear rates were significantly less for olive-oil and the olive-oil/CaF slurry compared with CaF alone. The microwear detail differed between the three lubricants. CONCLUSIONS: This study has shown that enamel wear can be reduced using dry or wet lubricants between opposing teeth that are worn under controlled conditions. Further research is required to clarify their possible clinical applications.

Analysis of Variance↗

PubMed2003

A model for the prediction of tooth wear in individuals.

BACKGROUND: Easily applied, age-specific standards are useful in assisting clinicians to decide whether the extent of tooth wear observed in a given patient at a specific age is acceptable or whether intervention is indicated. METHOD: A simple method of scoring tooth wear and previously established mathematical relationships between tooth wear scores and age, provide the basis of a method for predicting tooth wear scores. In its most specific form, the method can be used to predict tooth wear scores for individual patients at subsequent ages. Alternatively, tables or graphs can be consulted to provide a less precise prediction of tooth wear that can assist clinicians to decide whether the amount of wear reflects high, moderate or low rates of wear at the specified age. CONCLUSION: In cases where there is no reason to believe that aetiological factors have changed significantly over time, data obtained from the methods described can assist clinicians to plan appropriate management for patients presenting with unacceptable levels of tooth wear.

Age Factors↗

PubMed2000

Anxiety-related Stroop interference in adolescents.

A group of 16- to 18-year-old students was presented with threat-related and neutral Stroop stimuli on separate cards. Participants were assigned to anxiety groups on the basis of their scores on the Beck Anxiety Inventory (BAI; A. T. Beck & R. A. Steer, 1990). It was found, as predicted, that the high-anxiety group took significantly longer to identify the color of the threat-related word than the neutral words, whereas there was no difference for the low-anxiety group. There was a significant linear relationship between interference on the task and BAI scores, showing that as anxiety increases there is a corresponding increase in interference produced by the threat-related stimuli when compared with the neutral stimuli. This study demonstrates an anxiety-related Stroop interference effect for adolescents consistent with that reported in the adult literature.

Adolescent↗

PubMed1999

Experimental studies of human dentine wear.

Previous in-vitro studies have described the relation between rates of enamel wear and variables such as applied load and lubricant pH. The aim here was to extend understanding of tooth-wear processes by considering the rate of wear in human dentine. Enamel was removed from extracted third molar teeth that had been sectioned mesiodistally. Moisture fluctuation within dentine was minimized by conducting all procedures under copious irrigation or in sealed containers of lubricant at pH 7.0. Specimens were subjected to wear using a purpose-built apparatus at loads of 6.2, 9.95 and 13.2 kg. All experiments were done with a unidirectional wear stroke of 3 mm at a rate of 80 cycles/min for 75 min and repeated for 75 min. Dentine wear was assessed by specimen weight loss. At pH 7.0, wear rates ranged from 0.50 mg/10(3) cycles at a load of 6.2 kg to 0.77 mg/10(3) cycles when a load of 13.2 kg was applied. At higher loads, dentine wear rates were similar to those of enamel. Increasing load is thus associated with a progressive increase in the rate of dentine wear. This relation differs significantly from that for enamel, reflecting fundamental differences in the composition and structure of these tissues.

Biomechanical Phenomena↗

PubMed1998

Wear of human enamel: a quantitative in vitro assessment.

Many factors influence the extent and rate at which enamel wears. Clinical studies in humans are limited by difficulties in the accurate quantification of intra-oral wear and by a lack of control over the oral environment. The purpose of this study was to determine the wear characteristics of human dental enamel under controlled experimental conditions. An electro-mechanical tooth wear machine, in which opposing enamel surfaces of sectioned, extracted teeth were worn under various conditions, was used to simulate tooth grinding or bruxism. Enamel surface wear was quantified by weight to an accuracy of 0.1 mg, with water uptake and loss controlled. The variables considered included the structure and hardness of enamel, facet area, duration of tooth contact, relative speed of opposing surfaces, temperature, load, pH, and the nature of the lubricant. Enamel wear under non-lubricated conditions increased with increasing load over the range of 1.7 to 16.2 kg. The addition of a liquid lubricant (pH = 7) reduced enamel wear up to 6.7 kg, but when the load increased above this threshold, the rate of wear increased dramatically. With the viscosity of the lubricant constant and pH = 3, the rate of wear was further reduced to less than 10% of the non-lubricated rate at 9.95 kg, after which the rate again increased substantially. Under more extreme conditions (pH = 1.2, simulating gastric acids), the wear was excessive under all experimental loads. When saliva was used as a lubricant, the amount of wear was relatively low at 9.95 kg, but rapid wear occurred at 14.2 kg and above. These results indicate that under non-lubricated conditions, enamel wear remains low at high loads due to the dry-lubricating capabilities of fine enamel powder. Under lubricated conditions, low loads with an acidic lubricant lead to little enamel wear, whereas very low pH results in a high rate of wear under all loads.

Analysis of Variance↗

PubMed1997

Dental arch form in three Pacific populations: a comparison with Japanese and Australian aboriginal samples.

The purpose of this study was to provide information about arch shape variations among South Pacific populations. The application of Fourier transforms, Y(phi i) = ao/2 + sigma (aicos phi i + bisin phi i) was used to separate two components of variation; size and shape. Dental arch size can be described by one coefficient (ao), while the shape can be summarized by the first three harmonics (amp1-3) in the Fourier series. The materials used in this study were dental casts of South Pacific populations (Fiji, Western Samoa and Kiribati), Australian Aboriginals and Japanese. Fijians, Western Samoans and Kiribati people have larger upper and lower dental arches than that of Japanese. These populations were separated by the arch size and first Fourier amplitudes which showed the arch depth/width ratio. The Fijian upper and lower dental arches were significantly larger than those found in other populations and was characterized by a wide posterior arch breadth. The Western Samoan and Kiribati arch shape was more similar to the Japanese arch shape than the Fijian. Distribution patterns of arch shape characteristics in these populations showed the same tendencies in the upper and lower arches.

Female↗

PubMed1997

Cephalometric analysis of masseter muscle and dentoskeletal morphology in dentate and edentulous humans.

A study was done to clarify the attachment position of the superficial masseter muscle and its relationship with craniofacial morphology in dentate and edentulous subjects. Data were obtained from lateral cephalometric radiographs of a total of 39 cadavers in which the superficial masseter muscle had been defined with colloidal barium. Principal component analysis provided evidence that the lower masseter muscle width was associated with the size of the ramus, and related to the position of the anterior margin of the muscle. Linear discriminant function data suggested that ramus width, coronoid height and the distance between the anterior margin of the masseter muscle and the mandibular notch contributed most to the observed difference between dentate and edentulous subjects. The derived function correctly assigned 100% of dentate and 95% of edentulous subjects. The results of this study indicated that a reduction of masticatory function was associated with the position of the anterior border of the masseter muscle insertion and also with differences in ramus dimension, the most significant of which were differences in the coronoid process and gonial angle. In general, age was not a significant determinant of variation in superficial masseter muscle dimensions or orientation.

Age Factors↗

PubMed1996

Removable prosthodontics: a survey of practices and attitudes among South Australian dentists.

All dentists registered in South Australia were surveyed in July 1993 in relation to removable prosthodontics. The replies indicated that removable prosthodontics constituted a significant part of most dental practices. Most dentists felt that removable prosthodontics should be an essential part of the undergraduate curriculum. They felt that more expertise is now required to manage the treatment of the ageing population with either their first or replacement removable prostheses. The majority of dentists felt that their own undergraduate training had equipped them well to manage removable prosthodontic treatment for their patients; however, many helpful suggestions were made on areas that they thought required more emphasis.

Adult↗

PubMed1995

Genetic and environmental influences on facial profile.

Observed variation in facial morphology results from the influences of both genetic and environmental factors. To investigate the role of genetic influences on variation in facial profile, lateral photographs of 23 male and 19 female monozygous (MZ), and 15 male and 22 female dizygous (DZ) twin pairs were selected from the records of the South Australian Twin Study. Soft tissue landmarks and facial profiles were identified, traced and digitized. Linear and angular measures defined by the landmarks were calculated and a series of Fourier functions derived to describe the facial profiles. These Fourier amplitudes were interpreted in terms of the specific regions which they represented. Correlations within MZ pairs were consistently higher than within DZ pairs for both the facial dimensions and the Fourier amplitudes, providing evidence of significant genetic contribution to facial convexity, facial height and facial depth. Variability in nose and lip morphology appeared to be under stronger environmental influence.

Adolescent↗

PubMed1994

Relationship between attachment of the superficial masseter muscle and craniofacial morphology in dentate and edentulous humans.

Previous studies have described the importance of the interaction between the masticatory muscles and the craniofacial skeleton in the control of craniofacial growth. This study describes the attachment and orientation of the superficial masseter muscle and its relationship with craniofacial morphology in dentate and edentulous subjects. Data were obtained from lateral cephalometric radiographs of a total of 31 cadavers in which the superficial masseter muscle had been defined with liquid barium. The results provide evidence that the morphology of the superficial masseter muscle in the gonion region differed significantly between dentate and edentulous subjects, with the masseter being 2.7 mm wider and the gonion-anterior muscle border distance being 4.0 mm greater in dentate subjects. The complex relationship between craniofacial morphology and the dimensions and inclination of the superficial masseter muscle were most clearly evident in dentate subjects where the position of the anterior border was related to ramus dimensions and mandibular and occlusal plane angles. The association is much less clear in edentulous subjects where normal function was disturbed. In general, age was not a significant determinant of variation in superficial masseter muscle dimensions and orientation.

Age Factors↗

PubMed1993

Nature and frequency of dental wear facets in an Australian aboriginal population.

The nature and frequency of dental wear facets were studied in a sample of 18-year-old Aborigines, 28 males and 31 females, living at Yuendumu in the Northern Territory of Australia. Facet frequencies were scored indirectly using dental models for all permanent teeth, except third molars, and evidence of non-masticatory tooth grinding in eccentric jaw positions was also recorded. The interplay between attrition and abrasion in an individual over time was assessed by examining facet appearance on serial dental models obtained at approximately yearly intervals from 7 to 25 years of age. Facetting was found to be a very common feature of the Aboriginal dentitions, with frequencies ranging from around 65% for pre-molars to about 90% for molars. Evidence of extreme mandibular movement was noted in 93% of males and 100% of females. The longitudinal observations indicated that wear facet definition varied over time, apparently due to episodes of tooth grinding superimposed on continually-acting abrasive influences. These results show that facetting on teeth associated with extreme mandibular positions and, by inference, the related behaviour of tooth grinding or bruxism are very common features in dentitions of Australian Aboriginals living an essentially non-industrial way of life.

Adolescent↗

PubMed1993

Comparative study of craniofacial morphology in Japanese and Australian aboriginal populations.

A metric study of 71 Japanese and 106 Australian aboriginal precontemporary crania was undertaken using direct measurements and cephalograms. Compared with Australian aboriginals, the Japanese are characterized by smaller cranial length, cranial base length, nasal floor length, palatal length, mandibular dimensions (except symphysis height), facial depth, posterior face height, and facial profile angle and larger cranial breadth and height, maxillary breadth, palatal breadth, anterior face height, and occlusal and mandibular plane angles. These differences confirm the previously described brachycephalic tendency in aboriginals and the dolichocephalic form in the Japanese. The differences are also consistent with the expected functional differences between the Australian aboriginal hunter-gatherer group masticating more resistant food with larger, more anteriorly located, more powerful masseter muscles and the Japanese group masticating less resistant food with correspondingly less robust masticatory musculature. The results highlight the differences in craniofacial morphology between groups with different genetic backgrounds subjected to significantly different environmental influences.

Adolescent↗

PubMed1992

Brief communication: interproximal tooth wear: a new observation.

Microscopic observations were made of wear on the proximal surfaces of tooth crowns of Australian Aboriginals and whites. Typical wear facets displayed well-defined borders within which vertical or near vertical furrows, ranging from about 0.1 to 0.5 mm in width, were noted. Furrows on the interproximal surface of one tooth seemed to "interdigitate" with those on the proximal surface of the adjacent tooth. These observations are not consistent with the commonly-held view that interproximal tooth wear results from a buccolingual movement of adjacent teeth that maintain contact through mesial migration. Vertical or near vertical movement of teeth, possibly including a tipping action, must be an important factor, although the precise nature of the movement requires further investigation.

Humans↗

PubMed1992

A multivariate study of patients with temporomandibular joint disorder, atypical facial pain, and dental pain.

The multifactorial nature of oral and facial pain was investigated by the collection of clinical and psychologic data from 312 patients with either dental pain, temporomandibular joint disorder, or atypical facial pain. Significant differences between the groups in gender and age distribution, muscle and joint pain, radiographic joint changes, number of remaining teeth, pain duration, and aspects of the patients' perception of pain were evident. In addition, discriminant function analysis clearly differentiated between the three groups on the basis of both clinical and psychologic variables, emphasizing the multifactorial nature of oral and facial pain.

Adult↗

PubMed1992

Abrasion: an evolutionary and clinical view.

Abrasion is the type of wear produced on the tooth by the friction of exogenous material forced over the surface by incisive, masticatory and grasping functions. It is one of the four common processes that have affected the morphology of newly erupted teeth from the time they first evolved millions of years ago. While some observers have regarded tooth reduction as pathological, there is evidence from comparative and palaeontological studies which demonstrates that these processes are an essential part of the normal, continually changing relationship between the form and function of the dentition. To understand these precise mechanisms is important if one is to replicate nature's 'intentions' in clinical dental procedures.

Adaptation, Biological↗

PubMed1991

Relationships between age and dental attrition in Australian aboriginals.

Tooth wear scores (ratios of exposed dentin to total crown area) were calculated from dental casts of Australian Aboriginal subjects of known age from three populations. Linear regression equations relating attrition scores to age were derived. The slope of the regression line reflects the rate of tooth wear, and the intercept is related to the timing of first exposure of dentin. Differences in morphology between anterior and posterior teeth are reflected in a linear relationship between attrition scores and age for anterior teeth but a logarithmic relationship for posterior teeth. Correlations between age and attrition range from less than 0.40 for third molars (where differences in the eruption and occlusion of the teeth resulted in different patterns of wear) to greater than 0.80 for the premolars and first molars. Because of the generally high correlations between age and attrition, it is possible to estimate age from the extent of tooth wear with confidence limits of the order of +/- 10 years.

Adolescent↗

PubMed1991

Continuous tooth eruption in Australian aboriginal skulls.

Increases in the distance from the cemento-enamel junction to the alveolar crest (CEJ-AC) have often been attributed to senile atrophy of the bone or to the effects of periodontitis, without reference to the condition of the alveolar crest. This study investigated the relationship between CEJ-AC distance, tooth wear, gender, site of the CEJ-AC measurements, and age in 161 pre-white-contact Australian aboriginal skulls. Individual teeth were included in the study when there was no evidence of dehiscence, periodontitis, or abscess cavity formation in the supporting alveolar bone. The CEJ-AC distances increased as the severity of attrition increased; in male skulls, CEJ-AC distances were greater than in female skulls for all categories of tooth wear. In general, CEJ-AC distances measured on the mesial aspects of teeth were greater than those recorded distally; lingual distances generally exceeded buccal recordings. The best explanation of these findings and similar reports in the anthropological literature is that continuous tooth eruption occurred without the concomitant coronal movement of alveolar bone. This conclusion has significant ramifications for anthropological, epidemiological, and clinical studies which use the CEJ and AC as reference points when measuring periodontal attachment loss (periodontitis).

Age Factors↗

PubMed1990

Concepts of occlusion: Australian evidence.

Longitudinal studies of aboriginal children over a 20-year period have drawn attention to the wide variation in morphological features of the dentition and the way in which occlusal relationships develop. This paper summarizes some important determinants of optimal occlusal development, namely, tooth size relationships within and between dentitions, the patterns of alveolar growth, and tooth migrations during the transition from primary to permanent teeth and the nature of growth changes in the dental arches. Dental occlusion constantly changes throughout life in response to changing functional requirements. Observations limited to cross-sectional material provide an incomplete, and sometimes misleading, concept of dental occlusion and masticatory function.

Adult↗