The prevalence, etiology and management of tooth wear in the United Kingdom

A two-year clinical trial of enamel wear opposing 5Y-TZP and lithium disilicate crowns

STATEMENT OF PROBLEM

Clinical information on enamel wear opposing 5 mol% yttria-stabilized tetragonal zirconia polycrystal (5Y-TZP) or lithium disilicate crowns is lacking. Moreover, the effect of surface roughness on the wear of enamel antagonists remains unclear.

PURPOSE

The purpose of this clinical study was to quantify the vertical wear and total volume of wear while also measuring the surface roughness of antagonists at 6-month intervals over 2 years.

MATERIAL AND METHODS

A tooth-supported first molar 5Y-TZP Lava Esthetic Fluorescent Zirconia crown or an IPS e.max CAD lithium disilicate crown was randomly provided for 24 participants (n=12). The contralateral first molar and opposite teeth were the natural enamel controls. The crowns were fabricated using computer-aided design and computer-aided manufacturing (CAD-CAM) technology and then polished. The data were gathered every 6 months at recall appointments with an intraoral scanner and a polyvinyl siloxane impression. A 3-dimensional (3D) comparative software program was used to measure the maximum vertical and volume loss on opposing enamel, as well as on the enamel control on the opposite side of the mouth. The surface of epoxy resin replicas was analyzed using a scanning electron microscope. The surface roughness of the cusp replica was measured with a 3D laser microscope. The crown's antagonist enamel and natural enamel wear were compared using a 2-way repeated measure ANOVA (α=.05).

RESULTS

No significant difference was found in the average volume loss between the crown's antagonist enamel (ZTE 0.042 ±0.005 mm3, LTE 0.048 ±0.006 mm3) and the enamel control (ZCE 0.046 ±0.004 mm3, LCE 0.050 ±0.005 mm3) (P>.05). No significant difference was found in surface roughness between the crown's antagonist enamel (antagonist enamel of zirconia group [ZTE] 0.7 ±0.3 µm, antagonist enamel of lithium disilicate group [LTE] 0.6 ±0.3 µm) and the enamel control (enamel control of zirconia group [ZCE] 0.7 ±0.3 µm, enamel control of lithium disilicate group [LCE] 0.5 ±0.2 µm) in both zirconia and lithium disilicate groups (P>.05). Also, no correlation was found between the amount of wear and the roughness of the surface. The wear patterns observed on the opposing enamel surfaces of the monolithic zirconia and lithium disilicate materials were found to be similar to those seen on natural enamel.

CONCLUSIONS

A 2-year clinical investigation found that polished lithium disilicate and 5Y-TZP crowns did not affect enamel wear more than enamel against enamel, contrary to laboratory studies. Another finding revealed that surface roughness did not significantly affect wear.

3D quantitative analysis and SEM qualitative analysis of natural antagonist enamel opposing CAD-CAM monolithic zirconia or lithium disilicate tooth-supported crowns versus enamel opposing natural enamel

PURPOSE

This study aimed to evaluate the maximum vertical wear, volume wear, and surface characteristic of antagonist enamel, opposing monolithic zirconia or lithium disilicate crowns.

MATERIALS AND METHODS

The study comprised 24 participants (n = 12), who were randomly allocated to receive either a 5 mol% Y-TZP or a lithium disilicate crown in positions which would oppose the natural first molar tooth. The contralateral first molar along with its antagonist was considered as the enamel opposing natural enamel control. Data collection was performed using an intraoral scanner and polyvinylsiloxane impression. The means of the maximum vertical loss and the volume loss at the occlusal contact areas of the crowns and the various natural antagonists were measured by 3D comparison software. A scanning electron microscope was subsequently used to assess the wear characteristics.

Results

The one-year results from 22 participants (n = 11) indicated no significant differences when comparing the zirconia crown's antagonist enamel (40.28 ± 9.11 µm, 0.04 ± 0.02 mm3) and the natural enamel wear (38.91 ± 7.09 µm, 0.04 ± 0.02 mm3) (P > .05). Also, there is no significant differences between lithium disilicate crown's antagonist enamel (47.81 ± 9.41 µm, 0.04 ± 0.02 mm3) and the natural enamel wear (39.11 ± 7.90 µm, 0.04 ± 0.02 mm3) (P > .05).

Conclusion

While some studies suggested that monolithic zirconia caused less wear on opposing enamel than lithium disilicate, this study found similar wear levels to enamel for both materials compared to natural teeth.

Clinical factors to consider in definitive treatment planning for patients with tooth wear

Diagnosis, disease control and prevention are the precursors to successful definitive restorative treatment of pathological tooth wear. This case series illustrates how proposed key clinical features can influence treatment complexity and provide the clinician with a logical sequence of treatment options for definitive management of tooth wear.

Accuracy of the Intraoral Scanner for Detection of Tooth Wear

OBJECTIVE

The aim of this work was to study the accuracy of the intraoral scanner for detection of tooth wear in natural teeth by using micro-computed tomography (micro-CT) as a gold standard.

MATERIALS AND METHODS

Twenty premolars were prepared, fixed in acrylic blocks, and scanned with an intraoral scanner (iTero Element® 2) and micro-CT for baseline reference images before artificial tooth wear induction. The samples were then scrubbed with abrasive sandpaper 20 times and scanned with the intraoral scanner. They were then superimposed with the reference images utilising the "TimeLapse" feature of the scanner until the abraded area appeared yellow, indicating tooth surface loss in the 50-200 μm range. The same samples were then rescanned by micro-CT to measure the actual tooth surface loss. This procedure was repeated for the subsequent experimental tooth surface loss of 200-400 μm range (orange areas) and 400-750 μm range (red areas). The collected data were analysed for sensitivity, positive predictive value (PPV), and accuracy. Level of statistical significance was set at .05.

RESULTS

In the detection of experimental tooth surface loss, the specificity, PPV, and accuracy of the intraoral scanner were 98%, 98%, and 97%, respectively.

CONCLUSIONS

The iTero® intraoral scanner can be recommended to be a suitable screening tool for tooth wear in routine dental practice.

Reliability of qualitative occlusal tooth wear evaluation using an intraoral scanner: A pilot study

Dental wear analysis through the use of an intraoral scanner is a reality of modern dentistry. This study aimed to investigate the reliability of qualitative tooth wear evaluation through three-dimensional images captured with an intraoral scanner and compared to clinical and photographic examinations. Eighteen adult volunteers of both genders (18 to 55 years old) were submitted to clinical exams, intraoral photographs and intraoral scanning protocol using an optical scanner (TRIOS® Pod, 3Shape, Copenhagen, Denmark). Occlusal tooth wear, from second to second premolars, was measured by two evaluators and reevaluated after 30 days, according to a slight modification of the method described by Mockers et al. Weighted Kappa was used to measure intra and inter-examiner agreement. The Friedman test was used to verify the differences among methods. Random and systematic errors were assessed using Bland-Altman plots. All statistical analysis was performed with p<0.05. There was a substantive agreement for clinical (K = 0.75) and photographic exams (K = 0.79) and a moderate agreement for intraoral scanner analysis (K = 0.60) for inter-examiner evaluation. A substantial intra-examiner agreement was obtained for both evaluators. No significant difference between the methods was observed (p = 0.7343 for examiner 1 and 0.8007 for examiner 2). The Bland-Altman plot confirmed no systematic errors between the methods and a random error of 0.25 with the scanner method when compared to clinical assessment. All three methods showed reliability in qualitative occlusal tooth wear evaluation. Intraoral scanning seems to be a sound and reliable tool to evaluate tooth wear when compared to traditional methods, considering the lower inter-examiner agreement and the inherent limitations of this pilot study. Further research will be necessary in order to achieve more robust evidence.

Epidemiology of Erosive Tooth Wear, Dental Fluorosis and Molar Incisor Hypomineralization in the American Continent

Non-carious dental lesions such as developmental defects of enamel (DDE) and erosive tooth wear (ETW) are the subject of intensive research. This paper aims to give perspectives on both DDE, including dental fluorosis and molar incisor hypomineralization (MIH), and ETW, presenting epidemiological data from the Americas and associated diagnostic aspects. Besides, it is important to present evidence to guide the clinical assessment process, supporting the clinicians' management decisions towards better oral health of their patients. The overall increase in the worldwide prevalence of non-carious lesions discussed in this this paper may reflect the need of perceptual changes. Although the number of publications related to these conditions has been increasing in the last years, there is still a need for clinical diagnostic and management awareness to include these conditions in routine dental practice. Besides, it is important to provide recommendations for standardized clinical assessment criteria, improving the process and helping clinicians' adherence. In this sense, this paper discusses the most commonly implemented indices for each condition. Thus, despite the wide range of diagnostic indices, BEWE is proposed to be the index recommended for ETW assessment, Dean or Thylstrup &amp; Fejerskov indices for fluorosis and preferably the EAPD criteria (or modified DDE index) for MIH. Overall, non-carious lesions are a growing concern, and it is important to implement preventive measures that control their severity and progression, and accurate diagnosis by the dental clinician.

Tooth Wear: Best Evidence Consensus Statement

PURPOSE

The purpose of this Best Evidence Consensus Statement was to evaluate the impact of wear on teeth.

MATERIALS AND METHODS

A search updated last on the 07th October 2020 using the terms tooth wear, dental erosion, dental abrasion or dental attrition yielded 11,694 results. Limiting the search to clinical trials, cross-sectional investigations, randomized controlled trials, reviews, systematic reviews and meta-analysis yielded 1,769 results. Mechanistic in vitro studies were also added to the list of abstracts supplying additional information of the impact of wear on teeth. All abstracts were reviewed by two authors. Those relating to the focus question formed the evidence base which was used to formulate the response.

RESULTS

From the search results, 212 articles were related to the research question and 60 were included in this paper. Although tooth wear prevalence is over 30% of the population in early adulthood and increases as individual's age, the impact on the dentition is poorly investigated in longitudinal clinical studies. Wear on teeth can result in alterations in shape and potentially dentine hypersensitivity depending on the etiology. However, the process is slow and pulpal death is rare. The impact that tooth wear has on the patient depends on patient characteristics to a greater extent than the severity of wear.

CONCLUSIONS

Tooth wear is a common condition and part of the ageing process. Erosive tooth wear is a term which acknowledges that acids are normally linked to progression, but mechanical actions of attrition and abrasion will cause visible damage. The changes to the shape of teeth on the macro and micro levels are used to investigate the progression, prevention, etiology, and management. The biological impact of wear on teeth is relatively innocuous and management is often a patient driven process. This article is protected by copyright. All rights reserved.

Tooth surface loss: A review of literature

Objectives

Tooth surface loss (TSL) or tooth wear (TW) is an irreversible loss of hard tooth structure caused by factors other than those responsible for dental caries. TSL is observed clinically as attrition, abrasion, abfraction, and erosion. It may be associated with symptoms such as tooth hypersensitivity and function impairment, and may lead to change in the morphology of the affected tooth. However, it may also be asymptomatic, meaning the patient may not be aware of it. In this instance, the dentist is encouraged to make the patient aware of this issue.

The aim of this review is to provide an overview of the classification and management of TSL.

Material and methods

The PubMed (MEDLINE) search engine was used to gather the most recent information on TSL. The search was restricted to a five year period (1 September 2014–31 August 2019), and only English-language studies were included. A Boolean search of the PubMed dataset was implemented to combine a range of keywords: (Tooth surface loss OR tooth wear) AND (tooth attrition OR tooth Abrasion OR tooth erosion OR tooth abfraction OR non-carious cervical lesions) AND (humans). Studies were also obtained by manual searches and from Google Scholar.

Results

By this process, 560 articles and studies were obtained. More studies were also obtained by manual searches and from Google Scholar. The most relevant published studies were chosen and used in the current review. The selected articles are included in the reference list.

Conclusion

TSL is a clinical problem that dentists face on a daily basis. Therefore, a sound clinical approach by which TSL can be prevented and managed is essential. While this approach requires that dentists are knowledgeable about the issue, increasing public awareness of TSL is also vital.

In vitro investigation of human enamel wear by dental porcelain

BACKGROUND

Ceramic crown that fires the layering porcelain on zirconia corping is starting to be used due to aesthetic requirements. However, many ceramics are used, but wear characteristics are often unknown.

OBJECTIVE

This study was performed to investigate the wear of human enamel by porcelains, and to determine the influence of porcelain hardness, surface roughness and crystal of porcelain on the enamel wear.

METHODS

Enamel specimens were prepared from extracted human molar teeth. Porcelain specimens were prepared from Deguceram Gold, Vita Omega 900, and Cercon Ceram Kiss. Enamel wear volume was calculated and the porcelain wear depth, surface roughness and Vickers hardness was measured. Moreover, the observation of a crystal by scanning electron microscope and the crystal by X-ray diffraction were identified.

RESULTS

Omega 900 showed the smallest enamel wear volume and porcelain wear depth. The Vickers hardnesses of Omega 900 and Cercon Ceram Kiss were almost identical. Leucite was detected from Deguceram Gold and Omega 900, and Silica and Silicon Nitride were detected from Cercon Ceram Kiss.

CONCLUSIONS

The enamel wear is influenced not by the hardness of the porcelain but by the surface roughness, the size and shape of the crystal.

In vitro wear behavior between enamel cusp and three aesthetic restorative materials: Zirconia, porcelain, and composite resin

PURPOSE

The aim of this study was to identify the effects of three aesthetic restorative materials on the wear between tooth and restoration by a pin-on-disk manner.

MATERIALS AND METHODS

Six aesthetic restorative materials were used to prepare disk specimens for wear test, which were Lava Zirconia as zirconia group, Vintage MP and Cerabien ZR as veneering porcelain group, Gradia Direct microhybrid composite containing prepolymerized fillers, Filtek Z250 microhybrid composite containing zirconia glass and colloidal silica particles, and Filtek Z350 nanocomposite as composite resin group. Vertical loss of the worn cusp, change of the surface roughness of the restoration materials, and the surface topography were investigated after wear test under 9.8-N contact load.

RESULTS

The porcelain groups (Vintage MP and Cerabien ZR) caused the largest vertical loss of teeth when compared with those of the composite resin and zirconia groups, and Filtek Z250 microhybrid composite results in the second-largest vertical loss of teeth. The surface of Filtek Z350 nanocomposite was deeply worn out, but visible wear on the surface of the zirconia and Gradia Direct microhybrid composite was not observed. When the zirconia surface was roughened by sand-blasting, vertical loss of teeth considerably increased when compared with that in the case of fine polished zirconia.

CONCLUSION

It was identified that microhybrid composite resin containing a prepolymerized filler and zirconia with reduced surface roughness by polishing were the most desirable restorative materials among the tested materials to prevent the two-body wear between aesthetic restorative material and tooth.

Effect of zirconia polycrystal and stainless steel on the wear of resin composites, dentin and enamel

This study evaluated the effect of two antagonist substrates (Y-TZP/zirconia or stainless steel) on the wear rate and surface alterations of different composite materials and bovine tooth substrates (enamel and dentin). The wear rate of different composite materials (n = 20; two direct composite resins: HelioMolar - HM; Clearfil AP-X - CAP, three indirect composite resins: Estenia C&B - EST; Adoro - ADO; Sinfony - SFY, and one composite resin for direct/indirect restorations: Filtek Z250 - Z250), bovine enamel and dentin against two different antagonist materials (zirconia or stainless steel) into two mediums (two-body and three-body wear) were collected. After wear tests on ACTA wear machine, Scanning Electron Microscopy (SEM) analysis was performed to access the surface alterations. The wear data were evaluated by three-way ANOVA and Tukey post-hoc test (α = 0.05). The factors 'antagonist', 'medium', 'restorative materials', and the interaction of all factors grouped by two and integrated showed statistical significance on the wear rates. A two-body test depicted no difference among all composites and enamel for wear rate, while a three-body test depicted differences among composites directly related to the filler content: EST < Z250 = CAP < ADO = HM < SFY. Dentin always showed the highest wear rates and enamel the lowest rates. The presence of food bolus (three-body test) led to higher wear rates in comparison to an only aqueous medium (two-body test). SEM analysis showed that different materials present specific wear patterns, regardless of the medium and the antagonist considered. Differently from enamel, dentin substrate was intensively prone to wear, regardless of the antagonist/medium. Resin composite substrates presented intermediate wear rates, depending directly on their filler content (% in weight).

Factores de riesgo de la atrición dental severa: un estudio de casos y controles

Objetivo: identificar los factores de riesgo de la atrición dental severa en pacientes que acudieron a instituciones de atención odontológica, públicas y privadas, de la ciudad de Cuenca, Ecuador. Materiales y métodos: fueron analizados 237 pacientes adultos, 79 casos con atrición dental grados 2, 3 y 4, según el índice de Smith y Knight, y 158 controles con atrición grados 0 y 1. Se realizó un examen clínico y fotográfico para determinar la relación entre la atrición dental y factores como edad, sexo, procedencia, número de dientes residuales, pH salival y bruxismo. Resultados: los pacientes mayores de 25 años (OR= 2,47 IC= 1,41 – 4,35 X2= 10,21 p= 0,001), con menos de 20 dientes en boca (OR= 4,95 IC= 1,47 – 16,62 X2= 7,97 p= 0,004) y con bruxismo (OR= 2,64 IC= 1,45 – 4,81 X2= 10,49 p= 0,001) tienen más probabilidades de presentar atrición dental severa. Luego de una regresión logística binaria se confirmó dicha relación: pacientes mayores de 25 años (OR= 2,03 IC= 1,08 – 3,818) con menos de 20 dientes en boca (OR= 3,90 IC= 1,07 – 14,19) y con bruxismo (OR= 3,22 IC= 1,70 – 6,10); sin embargo, se observó una capacidad predictora muy baja de la variables ajustadas según el R–cuadrado de Cox y Snell (0,123) y el R–cuadrado de Nagelkerke (0,172). Conclusiones: edad avanzada, menor cantidad de dientes en boca y bruxismo aumentaron la posibilidad de presentar atrición dental severa en los pacientes analizados. Mientras que el sexo masculino, la procedencia rural y el pH salival crítico (menor a 6) no se comportaron como factores de riesgo

To Evaluate the Severity, Distribution of Occlusal Tooth Wear and its Correlation with Bite Force in Young North Indian Adults

AIM

To determine the severity and distribution of occlusal tooth wear among young North Indian adults and to evaluate the correlation of occlusal tooth wear with bite force.

MATERIALS AND METHODS

A total of 164 subjects were enrolled in the present study. Inclusion criteria included subjects with age range of 25-40 years having a full complement of natural dentition (excluding third molars), with no history of orthodontic treatment, FPD and trauma. Maxillary and mandibular casts of each subject were taken. Tooth wear score of anterior and posterior teeth of both the arches was calculated using a five-point (0 to 4) ordinal scoring system. The calculated tooth wear scores were then compared with data concerning age, sex, number of daily meals, vegetarian/non-vegetarian diet, Group function/Canine guided occlusion and bite force. Nonparametric (Mann-Whitney) test was used to determine the relationship between various factors and occlusal tooth wear. Spearman's correlation coefficient was used to determine the correlation between tooth wear and bite force.

RESULTS

After applying statistical analysis to the data collected, total tooth wear score of the whole sample was 30.07 ± 6.39. Anterior teeth had significantly higher wear score than posteriors (P < 0.01). Males showed significantly higher (P < 0.001) tooth wear in both arches factors such as bite force and age showed significant correlation with tooth wear (P=0.000), however, the number of meals taken per day did not show any significant correlation. Higher tooth wear loss was seen in non vegetarian dietary pattern but it was statistically insignificant. It was also found that Group function occlusion showed significantly higher mean tooth wear loss 45.76 ± 9.19 as compared to Canine guided occlusion 26.37 ± 10.68 (P=0.000).

In Vivo Electron Paramagnetic Resonance Tooth Dosimetry: Dependence of Radiation-Induced Signal Amplitude on the Enamel Thickness and Surface Area of Ex Vivo Human Teeth

In vivo L-band electron paramagnetic resonance tooth dosimetry is a newly developed and very promising method for retrospective biodosimetry in individuals who may have been exposed to significant levels of ionizing radiation. The present study aimed to determine the relationships among enamel thickness, enamel area, and measured electron paramagnetic resonance signal amplitude with a view to improve the quantitative accuracy of the dosimetry technique. Ten isolated incisors were irradiated using well-characterized doses, and their radiation-induced electron paramagnetic resonance signals were measured. Following the measurements, the enamel thickness and area of each tooth were measured using micro-focus computed tomography. Linear regression showed that the enamel area at each measurement position significantly affected the radiation-induced electron paramagnetic resonance signal amplitude (p < 0.001). Simulation data agreed well with this result. These results indicate that it is essential to properly consider enamel thickness and area when interpreting electron paramagnetic resonance tooth dosimetry measurements to optimize the accuracy of dose estimation.

Erosive and Mechanical Tooth Wear in Viking Age Icelanders

(1) Background: The importance of the Icelandic Sagas as a source of information about diet habits in medieval Iceland, and possibly other Nordic countries, is obvious. Extensive tooth wear in archaeological material worldwide has revealed that the main cause of this wear is believed to have been a coarse diet. Near the volcano Hekla, 66 skeletons dated from before 1104 were excavated, and 49 skulls could be evaluated for tooth wear. The purpose of this study was to determine the main causes of tooth wear in light of diet and beverage consumption described in the Sagas; (2) Materials and methods: Two methods were used to evaluate tooth wear and seven for age estimation; (3) Results: Extensive tooth wear was seen in all of the groups, increasing with age. The first molars had the highest score, with no difference between sexes. These had all the similarities seen in wear from a coarse diet, but also presented with characteristics that are seen in erosion in modern Icelanders, through consuming excessive amounts of soft drinks. According to the Sagas, acidic whey was a daily drink and was used for the preservation of food in Iceland, until fairly recently; (4) Conclusions: It is postulated that the consumption of acidic drinks and food, in addition to a coarse and rough diet, played a significant role in the dental wear seen in ancient Icelanders.

Effect of tooth whitening strips on fatigue resistance and flexural strength of bovine dentin in vitro

Objective

To determine the effects of whitening strips on bovine dentin fatigue resistance and flexural strength in vitro.

Materials and methods

A total of eighty bovine dentin specimens (2x2x17mm) were treated with either: control glycerine gel on plastic film wrap or whitening strips containing 9.5% hydrogen peroxide. Treatment was applied for 30 minutes, twice a day, for 1- or 4-weeks. After the last treatment, ten specimens per group were randomly selected to undergo fatigue testing (10⁶ cycles, 3Hz, 20N) while the other ten were subjected to flexural strength testing after ten days of storage in artificial saliva. Kaplan-Meier method with a log rank test, Wilcoxon test and Cox regression were used to assess fatigue test results (p<0.05). One-way ANOVA and Tukey’s tests were used to compare the flexural strength results (p<0.05).

Results

There were significant differences in survival during the fatigue test among the groups (p<0.001). Treatment (control or bleach) was a significant factor for specimen survival (p<0.001, Exp(B) = 33.45). There were significant differences in mean flexural strength (p<0.001). No significant difference was found between “1-wk control” and “4-wk control”. The mean flexural strength and fatigue resistance of the “4-wk bleach” were significantly lower than all the other groups.

Conclusions

The use of whitening strips reduced the fatigue resistance and flexural strength of bovine dentin in vitro. Until the effect of whitening strips on mechanical properties of human dentin is fully elucidated, it remains prudent to advise patients to avoid excessive direct use of whitening strips on dentin.

Supraesophageal Reflux: Validation of a Symptom Questionnaire

OBJECTIVES: To develop and validate a questionnaire for supraesophageal manifestations of reflux (SER) that will facilitate its study in clinical and research settings.

STUDY DESIGN: The Supraesophageal Reflux Questionnaire (SERQ) and previously validated Reflux Symptom Index (RSI) were subjected to multiple types of validity testing, including content validity, concurrent validity, reproducibility, and predictive validity.

RESULTS: The concurrent validity and reproducibility of both instruments was good to excellent for most items tested. The predictive validity of the SERQ was superior to the RSI when it included the covariates of history of sinusitis, use of over-the-counter antacid medications, age, gender, and body mass index.

CONCLUSIONS: The SERQ will serve as both a useful clinical and research tool by offering not only SER symptom information, like the RSI, but also information about the patient's medical history and medication usage that will facilitate use of the SERQ in research protocols.

EBM rating: B-2b

Assessment of oral hygiene habits, oral hygiene practices and tooth wear among fertilizer factory workers of Northern India: A Cross sectional study

BACKGROUND

The association between oral hygiene habits & practices and severity of tooth wear lesion varies from community to community and also from occupation to occupation. The present study was conducted with to assess oral hygiene habits & practices and tooth wear among fertilizer factory workers of Punjab, India.

MATERIAL AND METHODS

A descriptive cross sectional survey was conducted among 965 male workers who were aged between 19-58 years, who were the workers of fertilizers factory of Bathinda, India. An interview on the demographic profile, oral hygiene practices, and adverse habits followed a clinical examination for recording the Tooth Wear (Smith and Knight Index 1984) using Type III examination. The Chi-square test and a Stepwise multiple linear regression analysis were used for the statistical analysis. Confidence interval and p-value set at 95% and ≤ 0.05 respectively.

RESULTS

In the present study majority (47.2%) of the study population used chew sticks for cleaning their teeth. Overall prevalence of adverse habits was reported (92.4%). Study population showed higher prevalence of tooth wear (77.1%). Best predictors identified for Tooth Wear were oral hygiene practices, adverse habits, years of work experience and age respectively.

CONCLUSIONS

Considerable percentages of fertilizer factory workers have demonstrated a higher prevalence of tooth surface loss. This may be useful in designing the investigations that aim to further explore the causes for these findings and more importantly to plan oral health promotion program implementing both preventive and curative strategies.

KEY WORDS

Tooth wear, smith & knight index, fertilizer factory.

Influence of various acidic beverages on tooth erosion. Evaluation by a new method

MATERIAL & METHODS

We have analyzed the loss of enamel and dentine after exposure to different non-alcoholic drinks with a simple new method using bovine teeth. 100 enamel and 100 dentine specimens from freshly extracted bovine incisors were randomly attributed to 10 groups (n=10 for enamel and dentine each). Prior to the start of the experiment all specimens were weighed using a precision balance. The mean initial masses (SD) were 35.8 mg (7.2) for enamel and 24.7 mg (7.0) for dentine. No statistically significant differences were found between groups for initial masses (p>0.05, ANOVA with Bonferroni post hoc test). Thereafter, all specimens of one group were simultaneously placed in 200 ml of the following fluids: Coca-Cola, Coca-Cola light, Sprite, apple juice, Red Bull, orange juice, Bonaqua Fruits (Mango-Acai), tap water, chlorinated swimming pool water, and lemon juice. Fluids were continuously ventilated at 37° C for 7 days. Thereafter the specimens were weighed again and the mean mass loss was calculated.

RESULTS

The values were (enamel/dentine): Coca-Cola 7.5 mg/6.6 mg; Coca-Cola light 5.2 mg/3.5 mg, Sprite 26.1 mg/17.7 mg, apple juice 27.1 mg/15.2 mg, Red Bull 16.6 mg/17.0 mg, orange juice 24.3 mg/20.2 mg, Bonaqua Fruits (Mango-Acai) 17.8 mg/16.2 mg, tap water -0.2 mg/-0.3 mg, swimming pool water -0.3 mg/-0.2 mg, and lemon juice 32.0 mg/28.3 mg. From all drinks, Cola and Cola light showed the least erosivity (p<0.001, ANOVA with Bonferroni post hoc test) whereas lemon juice showed statistically significant higher erosivity than all other drinks except Sprite and apple juice (p<0.01, ANOVA with Bonferroni post hoc test).

CONCLUSIONS

In conclusion, erosivity of common non-alcoholic drinks varies widely. For example, Sprite, apple juice, and orange juice are about five times more erosive than Coca-Cola light. The findings from the present study should be taken into account in choosing a diet that provides satisfactory nutrition while minimizing tooth erosion.

Estimation of the rate of tooth wear in permanent incisors: a cross-sectional digital radiographic study

This study used conventional digital radiography to estimate the rate of tooth wear (TW) of maxillary and mandibular central incisors based on a cross-sectional study design. The crown length of 1239 permanent maxillary and mandibular central incisors from 346 persons (age groups: 10, 25, 40, 55 and 70 years ± 3) were measured by three calibrated dentists. Study teeth were intact incisally, had clearly visible incisal edges and cementoenamel junctions and had natural tooth antagonists. Measures were based on digital radiographic images (N = 666) archived in MiPACS within the electronic health record (axiUm(®)) from the College of Dentistry patient database. Incisor crown length decreased at a linear rate in both arches over the 60 years represented by the age groups. The average crown length for maxillary incisors in the youngest age group was 11.94 mm, which decreased by an average of 1.01 mm by median age 70. For mandibular incisors, the average crown length in the youngest age group was 9.58 mm, which decreased by an average of 1.46 mm in the oldest age group. Males and females showed similar rates of TW. Regardless of age, females demonstrated smaller mean crown height for maxillary incisors than males (P < 0.0001). Measures by the examiners demonstrated good agreement, with an interclass correlation coefficient of 0.869 and an average intra-examiner correlation of 99.5%, based on repeated measurements (n = 100). TW was estimated to average 1.01 mm for maxillary central incisors and 1.46 mm for mandibular central incisors by age 70 years.

Relationship of tooth wear to chronological age among indigenous Amazon populations

In indigenous populations, age can be estimated based on family structure and physical examination. However, the accuracy of such methods is questionable. The aim of this cross-sectional study was to evaluate occlusal tooth wear related to estimated age in the remote indigenous populations of the Xingu River, Amazon. Two hundred and twenty three semi-isolated indigenous subjects with permanent dentition from the Arara (n = 117), Xicrin-Kayapó (n = 60) and Assurini (n = 46) villages were examined. The control group consisted of 40 non-indigenous individuals living in an urban area in the Amazon basin (Belem). A modified tooth wear index was applied and then associated with chronological age by linear regression analysis. A strong association was found between tooth wear and chronological age in the indigenous populations (p <0.001). Tooth wear measurements were able to explain 86% of the variation in the ages of the Arara sample, 70% of the Xicrin-Kaiapó sample and 65% of the Assurini sample. In the urban control sample, only 12% of ages could be determined by tooth wear. These findings suggest that tooth wear is a poor estimator of chronological age in the urban population; however, it has a strong association with age for the more remote indigenous populations. Consequently, these findings suggest that a simple tooth wear evaluation method, as described and applied in this study, can be used to provide a straightforward and efficient means to assist in age determination of newly contacted indigenous groups.

The wear and tear of teeth

A review is presented of the mechanical damage suffered by tooth crowns. This has been the subject of much recent research, resulting in a need to revise some of the thinking about the mechanisms involved. Damage is classified here by scale into macro-, meso- and microfracture. The focus is on the outer enamel coat because this is the contact tissue and where most fractures start. Enamel properties appear to be tailored to maximize hardness, but also to prevent fracture. The latter is achieved by the deployment of developmental flaws called enamel tufts. Macrofractures usually appear to initiate as extensions of tufts on the undersurface of the enamel adjacent to the enamel-dentine junction and extend from there into the enamel. Cracks that pass from the tooth surface tend to be deflected by an enamel region of high toughness; if they find the surface again, a chip (mesofracture) is produced. The real protection of the enamel-dentine junction here is the layer of decussating inner enamel. Finally, a novel analysis of mechanical wear (microfracture) suggests that the local toughness of the enamel is very important to its ability to resist tissue loss. Enamel and dentine have contrasting behaviours. Seen on a large scale, dentine is isotropic (behaving similarly in all directions) while enamel is anisotropic, but vice versa on a very small scale. These patterns have implications for anyone studying the fracture behaviour of teeth.

Tooth wear against ceramic crowns in posterior region: a systematic literature review

The objective of this systematic review was to assess tooth wear against ceramic crowns in posterior region in vitro and in vivo. An electronic PubMed search was conducted to identify studies on tooth wear against ceramic crowns in posterior region. The selected studies were analyzed in regard to type of crowns, natural antagonist, measuring protocol and outcome. From a yield of 1 000 titles, 43 articles were selected for full-text analysis; finally, no in vitro and only five in vivo studies met the inclusion criteria. As there is heterogeneity in design, used measuring method, ceramics and analysis-form, a meta-analysis was not possible. Results of these studies are very controversial which makes a scientifically valid comparison impossible. This review indicated that some all-ceramic crowns are as wear friendly as metal-ceramic crowns. Up to now, it has been impossible to associate tooth wear with any specific causal agent. The role of ceramic surface treatment that might be responsible for the changing in rate of tooth wear seems undetermined as yet through clinical trials. The literature reveals that studies on this topic are subject to a substantial amount of bias. Therefore, additional clinical studies, properly designed to diminish bias, are warranted.

Influence of surface treatment on the wear of solid zirconia

OBJECTIVE

Recently there has been talk of the use of full-contour solid zirconia crowns or bridge restorations with no porcelain overlay. This could be a useful solution for patients with bruxism or limited interocclusal space. However, the hardness of zirconia could affect the opposite natural dentition. The aim of this in-vitro study was to investigate the role of surface treatments on the wear of a zirconia material and its antagonist.

MATERIALS AND METHODS

Fifty plates (10 × 10 × 1 mm) made of zirconia (LavaMulti(™) ZrO2, 3M ESPE), divided into five equal groups, were sandblasted and ground under standardized conditions with a fine-grit diamond bur (Komet Brasseler, Germany) to simulate clinical conditions. Group (a) was only fired, (b) was fired and sandblasted, (c) only ground, (d) was ground and additionally polished (EVE Ceramic Polishing-Set, Pforzheim) and (e) was ground and glazed. Wear behavior was measured with a pin-on-disk apparatus ABREX against 6 mm steatite balls as antagonists (45°, 5 N load, 5000 cycles, water). The amount of wear was determined topographically using a 3-D profilometer (Concept 3D, Mahr, Germany) by measuring the height loss of the antagonist and the depth of wear Pt of the zirconia.

RESULTS

In groups (a), (b), (c) and (d) the wear value Pt could not be determined (<1 μm). Wear values of the antagonists (steatite balls) revealed a similar outcome in contact with (b), (c) and (e) in the range of 81-85 μm, whereas (e) was more abrasive but not significantly. A noticeable difference in the wear of the antagonist showed group (d) to have the smallest value.

CONCLUSION

Polished zirconia seems to have the lowest wear on the antagonists, in contrast with the other kinds of surface treatment.

The signs and symptoms of tooth wear in a referred group of patients

AIM

To determine the prevalence of signs and symptoms in a group of tooth wear patients referred to a hospital-based consultant clinic.

METHOD

The clinical records of 290 patients referred to the Liverpool University Dental Hospital for tooth wear were reviewed retrospectively. A systematic sampling technique was used to select every alternate patient held on the consultant database.

RESULTS

There were significantly more males than females in a ratio of 2.3:1. Significantly more males (56%) presented with severe tooth wear compared with females (31%) (p <0.001). Aesthetic concerns were the most prevalent presenting complaint (59%) and sensitivity was the second most common presenting complaint (40%). Functional problems and pain were less prevalent at 17% and 14% respectively. Subjects who had lost posterior support had more severe wear and more worn anterior teeth, which was statistically significant (p = 0.001). The proportion of subjects with undiagnosed apical pathology on worn teeth was 13%.

CONCLUSIONS

Tooth wear predominated in males in this study. Patient dissatisfaction with appearance is the most common complaint and endodontic signs and symptoms are low in prevalence. Contrary to previous studies, lack of posterior support resulted in greater severity of wear, therefore restoring support is recommended.

Direct restorative treatment of anterior weared teeth after re-establishment of occlusal vertical dimension: a case report

OBJECTIVE

The loss of posterior teeth resulting in a lack of stability may lead to excessive mandibular load on some points of occlusion of the remaining teeth, causing wear. The rehabilitation of these cases must be carefully planned and the treatment requires a period of adaptation with a new vertical dimension.

BACKGROUND

This case report describes the treatment of a patient with a loss of almost all posterior inferior teeth and a consequential loss of occlusal vertical dimension and accentuated wear of anterior elements.

MATERIALS AND METHODS

  Provisional removable partial dentures were manufactured and the patient used them for a period of adaptation prior to restoration of the anterior teeth. After the patient's adaptation with the new occlusal dimension, anterior restorations were made using a mycrohibrid resin composite with different color aspects for an optimal stratification.

RESULTS

The restorations achieved an aesthetic configuration with ideal function as the final result and the occlusion showed a satisfactory stability for a provisional removable partial dentures.

CONCLUSION

This article presents an anterior direct rehabilitation approach not only as an alternative option, but also as viable and less expensive treatment option with an optimally aesthetic and functional result.

Clinical considerations for increasing occlusal vertical dimension: a review

The purpose of this article is to discuss the clinical considerations related to increasing the occlusal vertical dimension (OVD) when restoring a patient's dentition. Thorough extraoral and intraoral evaluations are mandatory to assess the suitability of increasing OVD. In the literature, multiple techniques have been proposed to quantify OVD loss. However, the techniques lack consistency and reliability, which in turn affects the decision of whether to increase the OVD. Therefore, increasing OVD should be determined on the basis of the dental restorative needs and aesthetic demands. In general, a minimal increase in OVD should be applied, though a 5 mm maximum increase in OVD can be justified to provide adequate occlusal space for the restorative material and to improve anterior teeth aesthetics. The literature reflects the safety of increasing the OVD permanently, and although signs and symptoms may develop, these are usually of an interim nature. Whenever indicated, the increase in OVD should be achieved with fixed restorations rather than a removable appliance, due to the predictable patient adaptation. The exception to this is for patients with TMD, where increasing the OVD should still be achieved using removable appliances to control TMD-associated symptoms before considering any form of irreversible procedure.

Dental erosion and its growing importance in clinical practice: from past to present

Since the mid-1990s, the focus of studies on tooth wear has steadily shifted from the general condition towards the more specific area of dental erosion; equally, a shift has occurred from studies in adults to those in children and adolescents. During this time, understanding of the condition has increased greatly. This paper attempts to provide a critical overview of the development of this body of knowledge, from earlier perceptions to the present. It is accepted that dental erosion has a multifactorial background, in which individual and lifestyle factors have great significance. Notwithstanding methodological differences across studies, data from many countries confirm that dental erosion is common in children and young people, and that, when present, it progresses rapidly. That the condition, and its ramifications, warrants serious consideration in clinical dentistry, is clear. It is important for the oral healthcare team to be able to recognize its early signs and symptoms and to understand its pathogenesis. Preventive strategies are essential ingredients in the management of patients with dental erosion. When necessary, treatment aimed at correcting or improving its effects might best be of a minimally invasive nature. Still, there remains a need for further research to forge better understanding of the subject.

Tooth wear and wear investigations in dentistry

Tooth wear has been recognised as a major problem in dentistry. Epidemiological studies have reported an increasing prevalence of tooth wear and general dental practitioners see a greater number of patients seeking treatment with worn dentition. Although the dental literature contains numerous publications related to management and rehabilitation of tooth wear of varying aetiologies, our understanding of the aetiology and pathogenesis of tooth wear is still limited. The wear behaviour of dental biomaterials has also been extensively researched to improve our understanding of the underlying mechanisms and for the development of restorative materials with good wear resistance. The complex nature of tooth wear indicates challenges for conducting in vitro and in vivo wear investigations and a clear correlation between in vitro and in vivo data has not been established. The objective was to critically review the peer reviewed English-language literature pertaining to prevalence and aetiology of tooth wear and wear investigations in dentistry identified through a Medline search engine combined with hand-searching of the relevant literature, covering the period between 1960 and 2011.

Cervical wear and occlusal wear from a periodontal perspective

The aim of this study was to investigate whether cervical wear was associated with occlusal wear and clinical periodontal parameters in relatively older adults. A total of 30 patients, with multiple non-carious cervical lesions (NCCLs) and without a disease or condition that could cause heavy tooth wear, were included in the study. The periodontal parameters including plaque index, probing pocket depth, gingival recession (GR) and tooth mobility were obtained from 641 teeth of which 475 (74·1%) displayed NCCLs. The levels of cervical wear and occlusal wear were determined according to a tooth wear index. Premolars were more likely to develop cervical wear than canines, molars and incisors. Cervical wear was significantly associated with less plaque accumulation and the presence of shallow pockets. The teeth with advanced GR and without increased mobility were 2·583 and 1·715 times more likely to develop deeper cervical lesions, respectively. Age and the level of occlusal wear were not linked to the bucco-lingual depth of cervical wear. In conclusion, the significant association of advanced cervical wear with the relatively healthy periodontal status suggested the role of abrasion and its possible combined action with erosion in the aetiology of NCCLs. The rate of GR and the lack of tooth mobility could constitute predisposing factors for the progression of cervical wear because the exposed root surfaces could be more susceptible to abrasion and/or erosion, and the non-mobile teeth resisting strongly against frictional forces, thus abrasive effects, could possibly develop cervical wear.

An experiment on the attrition of acid demineralized dentine in vitro

BACKGROUND

A laboratory investigation was designed to test the hypothesis that acids increase the rate of wear caused by attrition on dentine.

METHODS

Dentine sections from 10 teeth were polished, cleaned in an ultrasonic bath and divided into 8 equally sized areas. The occlusal tip of a tooth, placed vertically in a wear machine and loaded at 150 N, was moved against each dentine section for 5000 return strokes with artificial saliva acting as a lubricant. Each dentine section was divided into 8 sections and half randomly immersed in a 1% citric acid solution (pH 2.3) for 20 minutes. The wear regime produced 8 wear scars in total per dentine sample. The volume of each wear scar was measured using a contacting digitizing profilometer.

RESULTS

A total of 80 wear scars were produced with 40 treated with acid and 40 acting as controls. The mean for wear volume of the dentine scars with acid was 4.84 μm(3) (1.38) and for the non-acid surface 2.95 μm(3) (0.86). This difference was statistically significant (p < 0.05).

CONCLUSIONS

These results support the hypothesis that acids increase the rate of wear caused by attrition on dentine.

Tooth-wear patterns in adolescents with normal occlusion and Class II Division 2 malocclusion

INTRODUCTION

In this study, we investigated tooth-wear patterns in adolescents with either normal occlusion or Class II Division 2 malocclusion.

METHODS

The sample consisted of dental casts from 165 subjects that were divided into 2 groups: 115 normal occlusion subjects (mean age, 14.3 years) and 50 complete Class II Division 2 subjects (mean age, 13.9 years). Dental wear was assessed by using a modified version of the tooth wear index. The 2 groups were compared with the Mann-Whitney test for the frequency and severity of wear on each surface of each group of teeth. The level of statistical significance was set at 5%.

RESULTS

The normal occlusion group statistically had greater tooth wear on the incisal surfaces of the maxillary lateral incisors and the incisal surfaces of the maxillary canines than did the Class II Division 2 malocclusion group. The malocclusion group showed statistically greater tooth wear on the labial surfaces of the mandibular lateral incisors, the occlusal surfaces of the maxillary premolars and first molars, the occlusal surfaces of the mandibular premolars, the palatal surfaces of the maxillary second premolars, and the buccal surfaces of the mandibular premolars and first molars than did the normal occlusion group.

CONCLUSIONS

Subjects with normal occlusion and those with complete Class II Division 2 malocclusions have different tooth-wear patterns. Tooth wear on the malocclusion subjects should not be considered pathologic but, rather, the consequence of different interocclusal arrangements.

Dietary behavior and knowledge of dental erosion among Chinese adults

Objectives

To study the dietary behavior and knowledge about dental erosion and self-reported symptoms that can be related to dental erosion among Chinese adults in Hong Kong.

Methods

Chinese adults aged 25-45 years were randomly selected from a list of registered telephone numbers generated by computer. A telephone survey was administered to obtain information on demographic characteristics, dietary habits, dental visits, and knowledge of and presence of self-reported symptoms that can be related to dental erosion.

Results

A total of 520 participants were interviewed (response rate, 75%; sampling error, ± 4.4%) and their mean age was 37. Most respondents (79%) had ever had caries, and about two thirds (64%) attended dental check-ups at least once a year. Respondents had a mean of 5.4 meals per day and 36% had at least 6 meals per day. Fruit (89%) and lemon tea/water (41%) were the most commonly consumed acidic food and beverage. When asked if they ever noticed changes in their teeth, most respondents (92%) said they had experienced change that can be related to erosion. However, many (71%) had never heard about dental erosion and 53% mixed up dental erosion with dental caries.

Conclusion

Hong Kong Chinese adults have frequent intake of food and many have experienced symptoms that can be related to dental erosion. Their level of awareness of and knowledge about dental erosion is generally low, despite most of them have regular dental check-ups. Dental health education is essential to help the public understand dental erosion and its damaging effects.

Tooth-wear patterns in subjects with Class II Division 1 malocclusion and normal occlusion

INTRODUCTION

The aim of this study was to investigate the prevalence of tooth wear in adolescents with Class II malocclusion, compared with those with normal occlusion.

METHODS

The sample consisted of dental casts obtained from 310 subjects, divided into 3 groups: group 1, 110 subjects with normal occlusion (mean age, 13.51 years); group 2, 100 complete Class II Division 1 patients (mean age, 13.44 years); and group 3, 100 half-cusp Class II Division 1 patients (mean age, 13.17 years). Dental wear was assessed by using a modified version of the tooth-wear index. The 3 groups were compared by means of the Kruskal-Wallis and Dunn tests, considering the frequency and the severity of wear on each surface of each group of teeth. The level of statistical significance was set at 5%.

RESULTS

The normal occlusion group had statistically greater tooth wear on the palatal surfaces of the maxillary central incisors and the incisal surfaces of the maxillary canines than the corresponding surfaces in both Class II malocclusion groups. The complete and half-cusp Class II Division 1 malocclusion groups had statistically greater tooth wear on the occlusal surfaces of the maxillary second premolar and first molar, the occlusal surfaces of the mandibular premolars, and the buccal surfaces of the mandibular posterior teeth compared with the normal occlusion group. The half-cusp Class II Division 1 malocclusion group had significantly greater tooth wear on the incisal surfaces of the mandibular incisors compared with the complete Class II Division 1 malocclusion group.

CONCLUSIONS

Subjects with normal occlusion and complete or half-cusp Class II Division 1 malocclusions have different tooth-wear patterns. Tooth wear on the malocclusion subjects should not be considered pathologic but rather consequent to the different interocclusal tooth arrangement.

Comparison of in vitro erosion potentials between beverages available in the United Kingdom and the United States

OBJECTIVE

Our objective was to compare the physiochemical properties and erosion potentials between beverages available in the UK and the US.

METHODS

The physiochemical properties (pH, titratable acidity and fluoride concentration) and erosion potential on enamel surfaces of beverages available in the UK were compared to similar beverages from the US. Enamel windows were exposed to beverages for 25h. Teeth were sectioned through the windows, and lesion depths were defined as the average distance between the original tooth structure and the base of demineralization.

RESULTS

The pH was lower in UK apple juice, orange juice, Diet Pepsi and Sprite Zero (p<0.05), and higher in UK orange soda and diet orange soda than in similar US beverages (p<0.05). Titratable acidities were higher in UK apple juice, orange juice, orange soda, diet orange soda and Sprite (p<0.01), and lower in UK Sunny D than in the US counterpart (p<0.001). Fluoride concentrations were lower in UK apple juice, orange juice, Coke, and Diet Coke, Sprite and Sprite Zero (p<0.001), and higher in UK orange soda, diet orange soda, Pepsi and Diet Pepsi than in their US counterparts (p<0.001). Lesion depths were higher in UK apple juice, orange juice, Diet Coke, Sprite and Sprite Zero than in their US counterparts (p<0.05). Lesion depths were associated with pH (p=0.010) and country of origin (p=0.002).

CONCLUSIONS

Under similar laboratory conditions, the physiochemical properties and erosion potentials on enamel surfaces differed between some, but not all, beverages available in the UK and the US.

Wear of ceramic and antagonist—A systematic evaluation of influencing factors in vitro

OBJECTIVE

(1) To systematically review the existing literature on in vitro assessments of antagonist wear of ceramic materials; (2) To systematically evaluate possible influencing factors on material and antagonist wear of ceramic specimens.

METHODS

The database MEDLINE was searched with the terms "enamel," "wear" and "antagonist." The selected studies were analyzed with regard to wear parameters, type of antagonist and outcome. In the laboratory study, three ceramic materials were selected with different compositions and physical properties: IPS d.SIGN low-fusing metal ceramic, IPS Empress leucite ceramic, e.max Press lithium disilicate ceramic. These materials were subjected to the Ivoclar wear method (Willytec chewing simulator, 120,000cycles, 5kg weight) by systematically modifying the following variables which resulted in 36 tests with 8 specimens in each group: (1) configuration (flat, crown specimen), (2) surface treatment (polish, glaze), (3) type of antagonist (ceramic, two types of enamel stylus). Furthermore, the enamel styluses were cut to measure the enamel thickness and cusp width. Wear of both the material and the antagonist was quantified by scanning plaster replicas of the specimens with a laser scanner (etkon es1) and matching baseline and follow-up data with the Match 3D software (Willytec). The data were log-transformed to stabilize the variance and achieve near normality. To test the influence of specific test parameters, a four-way ANOVA with post hoc tests and Bonferroni correction was applied.

RESULTS

The systematic review revealed 20 in vitro studies in which a material and the antagonist wear of the same material was examined. However, the results were inconsistent mainly due to the fact that the test parameters differed widely. Most studies used prepared enamel from extracted molars as the antagonist and flat polished ceramic specimens. The test chamber was filled with water and some sort of sliding movement was integrated in the wear generating process. However, there was a huge variation in relation to the applied force, the used force actuator, the number of cycles, and the frequency of cycles per time as well as the number of specimens. The results of the systematic laboratory tests revealed that the following factors strongly influence the wear: configuration (more material wear of flat versus crown specimens), surface treatment (more antagonist wear of glazed versus polished specimens), the antagonist system (more material wear and less antagonist wear for ceramic stylus versus enamel stylus), and enamel thickness (less wear for thicker enamel). Material wear was not very much different between the materials. However, e.max Press generally caused more antagonist wear than the other two materials, which were quite similar. However, the main influencing factors did not yield consistent results for all the subgroups and there was a huge variability of results within the subgroups especially in those groups that used enamel as antagonist.

SIGNIFICANCE

As far as consistency and correlation with clinical studies is concerned, the set-up that consists of unprepared enamel of molar cusps against glazed crowns seems to be the most appropriate method to evaluate a ceramic material with regard to antagonist wear. However, due to the high variability of results large sample sizes are necessary to differentiate between materials, which calls the whole in vitro approach into question.