Dentine Wear Research Articles

Wear of human teeth: A tribological perspective

The four main types of wear in teeth are attrition (enamel-on-enamel contact), abrasion (wear due to abrasive particles in food or toothpaste), abfraction (cracking in enamel and subsequent material loss), and erosion (chemical decomposition of the tooth). They occur as a result of a number of mechanisms including thegosis (sliding of teeth into their lateral position), bruxism (tooth grinding), mastication (chewing), toothbrushing, tooth flexure, and chemical effects. In this paper the current understanding of wear of enamel and dentine in teeth is reviewed in terms of these mechanisms and the major influencing factors are examined. In vitro tooth wear simulation and in vivo wear measurement and ranking are also discussed.

Abrasion of eroded root dentine brushed with different toothpastes.

This study evaluated the surface roughness change and wear provided by different dentifrices on root dentine previously exposed to erosive challenges. According to a randomized complete block design, 150 slabs of bovine root dentine (6 x 3 x 2 mm) were ground flat and polished. In an area of 4 x 3 mm on the dentine surface, specimens were submitted to five erosive/abrasive events, each one composed by: exposure to Sprite Diet or distilled water for 5 min, then to a remineralizing solution for 1 min, and simulation of 5,000 brushing strokes. Four dentifrices--regular (RE), baking soda (BS), whitening (WT) and tartar control (TC)--and distilled water (CO), used as control, were compared. Final texture and the wear depth were evaluated using a profilometer. ANOVA did not show significant interaction, indicating that the effect of dentifrices on both surface roughness change and wear did not depend on whether or not the dentine was eroded ( p>0.05). There was no difference between abrasion of eroded and sound dentine. The Tukey's test revealed that WT, BS and TC provided the highest increase in surface roughness differing from RE and CO. TC yielded the deepest wear of root dentine, whereas RE and CO, the shallowest. No significant difference in wear among BS, TC and WT were observed. Within the limitations of this study, the data showed that abrasion of both eroded and sound root dentine was dependent on the dentifrice used.

Brushing Abrasion of Softened and Remineralised Dentin: An in situ Study

The aim of the present in situ study was to evaluate the effect of different periods of intra-oral remineralisation on the susceptibility of softened dentin to toothbrushing abrasion. Groups of 6 human dentin specimens (A–F) were recessed in the buccal aspects of intra-oral appliances which were worn for 21 days by 11 volunteers. The samples were demineralised twice a day extra-orally in the acidic beverage Sprite Light (pH 2.9) for 90 s. Subsequently, the dentin specimens were brushed at different times. Specimen A was brushed immediately after demineralisation. Specimens B–E were brushed after the intra-oral appliances had been worn for various periods in the mouth: specimen B for 10 min, C for 20 min, D for 30 min and E for 60 min. Specimen F was not brushed (control). After 21 days, dentin wear was measured with a profilometer. The following values (means ± standard deviation) were recorded (µm): A, 23.6 ± 16.7; B, 37.9 ± 29.7; C, 31.8 ± 26.5; D, 18.5 ± 10.5; E, 15.3 ± 11.6; F, 12.6 ± 6.7. There was a statistically significantly increased dentin loss for groups A, B and C as compared to the controls (U test: p < 0.05). However, after intra-oral periods of 30 and 60 min, wear was not significantly higher than in unbrushed controls. It is concluded that for protection of dentin surfaces at least 30 min should elapse before toothbrushing after an erosive attack.

Can tooth brushing damage your health? Effects on oral and dental tissues

Circumstantial evidence based on anecdote, case reports, epidemiological data and studies in vitro and in situ implicate tooth brushing with toothpaste with tooth wear, gingival recession and dentine hypersensitivity. This review attempts to assess the clinical significance of the potential harm produced by this most common oral hygiene habit. The toothbrush alone appears to have no effect on enamel and very little on dentine. Most toothpaste also has very little effect on enamel and in normal use would not cause significant wear of dentine in a lifetime of use. Wear of enamel and dentine can be dramatically increased if tooth brushing follows an erosive challenge. Gingival recession has a multi-factorial aetiology and certain individuals and specific teeth may be predisposed to trauma from tooth brushing. Tooth brushing is known to cause gingival abrasions but how these relate to gingival recession is not known. The role of toothpaste in gingival abrasion and recession surprisingly has received little if any attention. Gingival recession most commonly exposes dentine and localises sites for dentine hypersensitivity. Some toothpaste products can expose dentinal tubules but erosion is probably the more dominant factor in dentine hypersensitivity. There is no evidence to indicate that electric and manual toothbrushes differ in effects on soft and hard tissues. It is only under, over or abusive use or when combined with erosion that significant harm may be thus caused. In normal use it must be concluded that the benefits of tooth brushing far out-way the potential harm.

The role of toothpastes and toothbrushes in the aetiology of tooth wear

Objectives : To review current knowledge with respect to the epidemiology of abrasive lesions and the evidence for the role of toothpastes and toothbrushes in their aetiology. Materials and methods : ‘Medline’ databases for the period 1966 to the present day were searched electronically, while the dental literature prior to 1966 was searched manually. In both cases, the key words: tooth abrasion, toothpaste and toothbrush were used. Conclusions : Studies in vitro demonstrate that tooth brushing with abrasive toothpastes produces wear to dentine. Extrapolation of these data to effects in vivo is difficult, but suggests that, under normal use, tooth brushing with toothpaste will cause limited wear of dentine in a lifetime’s use. Negligible damage to dentine occurs with a toothbrush alone. Most toothpastes have low relative enamel abrasivity values and, alone, have little or no effect on enamel. Abuse and/or interaction with erosion can increase wear of dentine to pathological levels. Enamel softened by erosive agents is easily removed by any mechanical action.

Cervical tooth wear and sensitivity: erosion, softening and rehardening of dentine; effects of pH, time and ultrasonication.

Cervical dentine wear is commonly observed and may be associated with dentine hypersensitivity. Erosion is thought to play a part in both conditions but compared to enamel has been little studied in dentine. The aims of these studies in vitro were to: (i) determine the effects of citric acid on dentine at different pH values and over time; (ii) measure the depth of dentine demineralisation or softening using ultrasonication; (iii) determine whether softened dentine can be remineralised or rehardened using artificial saliva. Groups of flat dentine specimens prepared from unerupted human third molar teeth were: (a) exposed to citric acid at pH 3.2 for periods up to 4 h with mineral water as control; (b) exposed to citric acid at pH 2.54, 3.2, 4.5, 5.5 and 6.0 for 2 h and then subjected to ultrasonication stepwise up to 480 s; (c) exposed to citric acid at pH 2.54, 3.2, and 4.5, placed into artificial saliva for 24 h and then subjected to ultrasonication as in (b). Loss of dentine was measured by profilometry, after, each phase of erosion, ultrasonication and immersion in artificial saliva. Depth of erosion significantly increased non-linearly with time and significantly decreased with increasing pH. Ultrasonication had minimal albeit significant effects on control specimens. Removal of softened dentine increased with ultrasonication time. Depth of softening significantly increased with increasing erosion time to 2 h, plateauing at 2 microm. Depth of softening increased to 2 microm from pH 2.54 to pH 3.2 and decreased at higher pH values thereafter. 24 h in artificial saliva provided no protection to the soften zone against ultrasonicaion. Citric acid at all pH values and exposure times removed the dentine smear layer to expose tubules. Ultrasonication did not remove the smear layer on control specimens but removed all deposits formed after exposure to artificial saliva. It is concluded that dentine is susceptible to erosion even at relatively high pH, the tubule system is readily exposed and dentine, unlike enamel, shows little propensity to remineralise.

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.

Occlusal variables, bruxism and temporomandibular disorders: a clinical and kinesiographic assessment.

Seventy-five patients suffering from myofascial pain, headaches and anterior disc displacement were assessed clinically and with a kinesiograph. Twenty-eight asymptomatic dental staff served as a control group. The prevalence of awareness of bruxism was significantly greater in our TMD patients than the controls. Bruxism patients recorded a higher prevalence of incisor dentine wear suggestive of a forward mandible posture. Class II, Division 1 malocclusions formed a significantly higher proportion of the TMD patient group than the controls. Kinesiographic recordings showed that the vertical and lateral components of movement from postural position to intercuspal were significantly greater in the patient group.

Prevalence and severity of incisal and occlusal tooth wear in an adult Swedish population.

The material consisted of 585 randomly selected dentate individuals from the community of Jönköping, Sweden, who in 1983 reached the age of 20, 30, 40, 50, 60, 70, or 80 years. The degree of incisal or occlusal wear was evaluated for each single tooth in accordance with the following criteria: 0 = no wear or negligible wear of enamel; 1 = obvious wear of enamel or wear through the enamel to dentin in single spots; 2 = wear of dentin up to one-third of the crown height; 3 = wear of dentin more than one-third of the crown height and/or excessive wear of tooth restorative material. Among the 20-year-olds 35% of the subjects had no or slight incisal or occlusal wear. The corresponding figures for the 30- to 80-year age groups were 20%, 32%, 18%, 14%, 26%, and 23%, respectively. For the age groups 20-80 years, the percentage of teeth with incisal or occlusal wear in accordance with criteria 1-3 was 13%, 20%, 16%, 24%, 23%, 23%, and 23%, respectively. Men presented more teeth with wear than women, the difference being significant for all age groups except the 20- and 60-year-olds. Among the 20-year-olds 6% had one or more teeth with wear scored 2. Among subjects aged 30 and 70 years 10% and 31%, respectively, showed tooth wear with score 2. Wear with score 3 was only found in 2% of the total population. There was an increase in the number of teeth with incisal or occlusal wear with age. With increasing age, there was also a change in distribution of wear within the dentition.

Dependence of rate of physical erosion on orientation and density in mineralised tissues.

Bone, dentine and enamel samples were treated with a gas-propelled jet of an abrasive, NaHCO3, which is physically much softer than any of these tissues in their fully mineralised condition. It was nevertheless found that they are all eroded by this treatment, which can therefore be used as a new kind of qualitative test of physical properties relating to wear resistance. General correlations were found between both degree of mineralisation and between structure orientation and erosion rate, surface-parallel-feature zones being worn more rapidly. Bone domains with surface-parallel collagen were eroded faster than those with perpendicular lamellae even if they were more densely mineralised. Rates of dentine wear depended on both density and tubule orientation, with peritubular zones and better mineralised incremental layers being more resistant. Enamel tufts wear more rapidly than the surrounding well mineralised regions. Enamel diazones wear less than parazones (areas with surface parallel prisms). At the prism scale, enamel is removed more rapidly near prism boundary discontinuities and in tubular enamel, at tubule walls. As regards the common orientation dependent effects seen in these three tissues, a cohesive explanation would be that structure discontinuities can be better exploited in a wear process if they allow cleavage from the surface; which tendency will increase with parallelism to the surface.

Clinical Investigation of the Effects of Dentifrices on Dentin Wear at the Cementoenamel Junction

A two-year clinical study was conducted in vivo to assess the dentin wear caused by dentifrices; results were correlated and compared with those obtained in vitro.

A comparison of dentine wear on prepared tooth sections in vivo using two toothpastes

A comparison of dentine wear on prepared tooth sections in vivo using two toothpastes

Effect of Toothbrush Variables on Wear of Dentin Produced by Four Abrasives

A study was conducted to explore the effect of brush brand, brush hardness, and the concentration of abrasive on the wear of human dentin by four dentifrice abrasives. The two hard brushes produced similar and high levels of abrasion, whereas the two medium brushes of the same brands gave dissimilar and lower levels of abrasion. Dilution changed the ranking of two of the four abrasives.

Reduction in dentin wear resistance by irradiation and effects of storage in aqueous media.

Electromechanical dentin abrasion measurements showed that the irradiation treatment applied before radiotracer dentin abrasion measurements reduced the wear resistance of dentin. This caused changes in the measured relative abrasitivities of dentifrices. Effects of storage in aqueous media were also investigated.

The abrasive wear resistance of human dental tissues

Almost all dentifrices contain abrasives to assist in cleaning the teeth and some of the essential requirements of such abrasives are described. The wear resistance of dental tissues under hard and soft abrasives is discussed in relation to the appearance of a critical size effect and the degree of brittle fracture associated with the abrasion. The influence of the relative hardness of enamel to abrasive on the transition from “hard” to “soft” abrasion is examined and compared with that of metals. Using a radiotracer technique and a machine to simulate oral brushing, a study of the rates of wear of enamel and dentine and their inter-relationship with brush fibre geometry and dentifrice concentration has been made. The significance of these factors in dentifrice testing and formulation is discussed. It is shown that dental tissues exhibit marked transient wear phenomena. Some current experiments are described in which it is hoped to be able to determine the absolute rates of human tissue wear under in vivo conditions.