Wear of materials used in dentistry: a review of the literature

Effect of different ceramic systems on antagonist dental structure by microtomographic analysis

OBJECTIVES

This study aims to identify the two-dimensional and three-dimensional analyses and evaluate the loss of tooth structure in the tooth's different constituent elements and the ceramic antagonist's surface.

METHODS

In this study, three groups (n = 10) represented by different ceramic systems (lithium disilicate [GDis], lithium silicate reinforced with zirconia [GSil], and monolithic zirconia [GZir]) were evaluated. Each group obtained ten ceramic blocks and submitted them to the sintering/crystallization process. To carry out the wear test, healthy mandibular premolars were used as the specimens and the ceramic blocks as antagonists. The premolars were submitted to two-dimensional and three-dimensional analyses using a computerized microtomography (µTC) before and after the wear test. The wear test was performed with 30 N and 300,000 cycles load, with occlusion, laterality, and disocclusion movements.

RESULTS

The statistical analysis comparing the loss of two-dimensional tooth structure showed a statistically significant difference among all groups (p < 0.05). Statistical analysis comparing the percentage of loss of three-dimensional tooth structure showed a statistically significant difference between groups GDis and GSil and between groups GDis and GZir. However, when comparing GSil with GZir, no statistically significant difference was found. The qualitative analysis of the teeth showed that GDis showed considerable enamel loss and dentin exposure, GSil showed enamel wear with flattening the cusp without dentin exposure, and GZir showed minimal enamel wear without dentin exposure. In the qualitative analysis of ceramic antagonists, more significant wear of the ceramic material for GDis was observed, followed by the GSil and GZir groups, respectively.

SIGNIFICANCE

The use of the lithium disilicate should be cautious, restricting it to areas with lower masticatory forces. Areas of higher masticatory forces showed a large amount of antagonist wear, with dentin involvement. This can lead to dentinal hypersensitivity, risk of compromising patients' occlusion, by harming group disocclusion guides, causing pain and temporomandibular disorders.

The Influence of Abrasive and Acidic Aggressions on the Surface Condition of Flowable Composite Resin

The aim of this in vitro study was to evaluate the effect of hydrochloric acid associated with the abrasive effect of toothbrushing on the surface condition of three flowable composite resins used for direct restoration. Seventy samples of each composite resin: Grandio Flow (VOCO, Germany)—group A, Filtek Ultimate Flow (3M-ESPE, MN, USA)—group B, G-aenial Flo X (GC Europe)—group C were prepared, submersed in hydrochloric acid 30% for 60 min and then submitted to simulated toothbrushing procedure using 5000 cycles with toothbrushes with medium and hard bristles, immediately after the chemical attack, after 30 min or without any chemical attack. The sample’s surface roughness was analyzed using a noncontact profilometer (Dektak XT, Bruker, USA). ANOVA and post hoc Bonferroni tests, with a p < 0.05, were used to analyze the values. Hydrochloric acid action for 60 min and six months of toothbrushing using toothbrushes having medium hardness or firm bristles affects the surface roughness of tested flowable composite resins. Toothbrushing with firm bristles immediately after acidic challenge determines increased surface roughness for two of the three flowable composite resins (Grandio Flow and Filtek Ultimate Flow). Toothbrushing with medium or firm bristles thirty minutes after the acidic aggression determine no effect on surface condition of flowable composite resins.

Risk Indicators Affecting the Survival of the Mandibular First Molar Adjacent to an Implant at the Mandibular Second Molar Site: A Retrospective Study

This study aimed to compare the survival of mandibular first molars (MnM1s) adjacent to implants placed in mandibular second molar sites (ImM2s) with MnM1s adjacent to mandibular second molars (MnM2s) and to investigate risk indicators affecting the survival of MnM1s adjacent to ImM2s. A total of 144 patients who had MnM1s adjacent to ImM2s and MnM1s adjacent to MnM2s on the contralateral side were included in this study. Clinical variables and radiographic bone levels were evaluated. The survival of MnM1s adjacent to ImM2s or MnM2s was evaluated using a Kaplan–Meier analysis and Cox proportional hazards model. The 5-year cumulative survival rates of MnM1s adjacent to ImM2s and MnM2s were 85% and 95%, respectively. MnM1s adjacent to ImM2s of the internal implant-abutment connection type had higher multivariate hazard ratios (HR) for loss. MnM1s that had antagonists with implant-supported prostheses also had higher HR for loss. The multivariate HR for the loss of MnM1s adjacent to ImM2s with peri-implant mucositis was 3.74 times higher than MnM1s adjacent to healthy ImM2s. This study demonstrated several risk indicators affecting the survival of MnM1s adjacent to ImM2s. It is suggested that supportive periodontal and peri-implant therapy combined with meticulous occlusal adjustment can prolong the survival of MnM1s and ImM2s.

Wear resistance of crowns made from different CAM/CAD materials

OBJECTIVES

The aim of this laboratory study was to evaluate the wear resistance of crowns made from current computer-aided design and computer-aided manufacture (CAD/CAM) materials. In addition, the abrasion of the steatite antagonist against these materials was compared.

METHODS

Identically shaped crowns of lithium disilicate, zirconia-reinforced lithium disilicate and a polymer-infiltrated ceramic network (PICN) were fabricated with an occlusal thickness of 1.5mm and a lateral wall thickness of 1.2mm (n=8). The crowns were cemented with a dual-polymerizing luting resin on composite resin dies. Using spherical steatite antagonists, all specimens were loaded with 49N for 1,200,000 cycles in a mastication simulator with additional thermocycling. After 120,000, 240,000, 480,000, 960,000, and 1,200,000 cycles, precision impressions were made and investigated with a laser scanning microscope. The vertical and volume substance loss was measured. Additionally, the substance loss of the antagonists was evaluated after 1,200,000 loading cycles.

RESULTS

No significant difference (p>0.05) was found in the median volume loss of the test materials after 1,200,000 cycles (lithium disilicate: 0.405mm³, PICN: 0.362mm³, zirconia-reinforced lithium disilicate: 0.340mm³). The vertical substance loss of PICN (157μm) was significantly lower (p≤0.05) than that of lithium disilicate (201μm) and zirconia reinforced lithium disilicate (191μm). However, the substance loss of steatite against zirconia-reinforced lithium disilicate (0.191mm³) was significantly lower (p≤0.05) than against lithium disilicate (0.296mm³) and PICN (0.531mm³).

SIGNIFICANCE

All three CAD/CAM materials showed wear resistance that seems appropriate for clinical application. Also, the abrasion of the antagonist looks promising.

Assessment of Force Retention between Milled Metallic and Ceramic Telescopic Crowns with Different Taper Angles Used for Oral Rehabilitation

The present study assessed the retention forces corresponding to different telescopic systems used in removable prosthetic dentures. The telescopic systems were represented by Co–Cr alloy or zirconia-based primary crowns and Co–Cr secondary crowns. All crowns were manufactured using computer-aided design/computer-aided manufacturing technology (CAD/CAM). Two types of reference abutment teeth (upper canine and first upper molar) were selected in order to obtain the telescopic crowns and two taper angles—of 0° and 2°—were used for the design of the crowns. A number of 120 samples of telescopic crowns were obtained and subjected to mechanical tests, following a specific protocol, on a mechanical testing equipment. The retention of the telescopic systems was evaluated for different sets of cycles (up to 360), represented by movements that simulate the intraoral insertion and disinsertion of the telescopic systems. The present study highlights that the telescopic systems in which the primary crown is made of zirconia ceramics presents more advantages than those made of Co–Cr. All telescopic systems studied, highlighted that by modifying the taper angle from 0° to 2°, the retention forces have decreased, irrespective of the materials used for the fabrication of the primary crown, suggesting that by using a taper angle of 0°, which is known to be ideal, more efficient, and reliable prosthesis can be developed. Thus, even though the ceramic–metallic telescopic system exhibited the highest retention, all telescopic crowns evaluated registered values between 2–7 N, indicating that they are suitable for clinical use.

Changes in tribological and antibacterial properties of poly(methyl methacrylate)-based 3D-printed intra-oral appliances by incorporating nanodiamonds

It is essential for 3D-printed intra-oral appliances to be able to withstand the mechanical and microbial insult existent in the harsh environment of the oral cavity. Poly(methyl methacrylate) (PMMA)-based appliances are widely used in dentistry. Hence, the present study aimed to evaluate the role of nanodiamonds (NDs) as fillers to enhance the resistance to friction and wear. Using a solution-based mixing technique, 0.1 wt% ND was incorporated into the PMMA, and specimens were 3D-printed for tribological and bacterial analysis. The control specimens without ND fillers were tested against specimens with both amine-functionalized NDs (A-ND) and pure non-functionalized NDs (ND). The surface hardness test revealed a statistically significant increase in the Vickers micro-hardness (p < 0.001) in the nanocomposite groups. There was a significant reduction in the coefficient of friction (COF) (p < 0.01) in both the ND and A-ND nanocomposites compared to the stainless steel (SS) counter surfaces. However, for titanium (Ti)-based specimens, the COF of the control group was similar to that of A-ND but lower than that of ND. The wear resistance evaluation revealed that both the ND and A-ND groups displayed enhanced resistance to surface loss in comparison to the controls for both SS and Ti counter-surfaces (p < 0.001). Furthermore, both A-ND and ND exhibited significantly enhanced resistance to the formation of Streptococcus mutans biofilms after 48 h (p < 0.01) compared to the control group. Hence, we concluded that the addition of 0.1 wt% ND in the PMMA-based resin for 3D printing resulted in significant improvement in properties such as COF, wear resistance, and resistance to S. mutans, without any notable impact associated with the functionalization of the NDs.

In Vitro Simulation and In Vivo Assessment of Tooth Wear: A Meta-Analysis of In Vitro and Clinical Research

Tooth wear may be described as a side-effect of occlusal forces that may be further induced by the common use of contemporary prosthetic materials in practice. The purpose of this systematic review was to appraise existing evidence on enamel wear from both in vitro and clinical research and explore whether evidence from these study designs lies on the same direction. Five databases of published and unpublished research were searched without limitations in August 2019 and study selection criteria included in vitro and clinical research on enamel tooth wear. Study selection, data extraction, and risk of bias assessment were done independently and in duplicate. Random effects meta-analyses of standardized mean differences (SMDs) or weighted mean differences (WMDs) with 95% confidence intervals (CIs) were conducted while a Monte Carlo permutation test for meta-regression on the exploration of the effect of the study design on the reported outcomes was planned. A total of 27 studies (23 in vitro and 4 clinical) were eligible while 12 contributed to meta-analyses. Overall, some concerns were raised for the quality of the existing evidence and the potential for risk of bias. Enamel wear (mm) of antagonist teeth was more pronounced when opposed to conventional porcelain compared to machinable ceramics (SMD = 2.18; 95%CIs: 1.34, 3.02; p < 0.001). Polished zirconia resulted in decreased volumetric enamel wear (mm³) of opposing teeth compared to pure natural enamel (SMD = –1.06; 95%CIs: –1.73, –0.39; p = 0.002). Monolithic zirconia showed evidence of enhanced potential for antagonist wear (μm) compared to natural teeth (WMD = 107.38; 95%CIs: 30.46, 184.30; p = 0.01). Study design did not reveal an effect on the tooth wear outcome for the latter comparison when both clinical and in vitro studies were considered (three studies; Monte Carlo test, p = 0.66). In conclusion, there is an overriding need for additional evidence from clinical research to substantiate the findings from the already existing laboratory simulation studies.

Advancements in all-ceramics for dental restorations and their effect on the wear of opposing dentition

Tooth wear is a process that is usually a result of tooth to tooth and/or tooth and restoration contact. The process of wear essentially becomes accelerated by the introduction of restorations inside the oral cavity, especially in case of opposing ceramic restorations. The newest materials have vastly contributed toward the interest in esthetic dental restorations and have been extensively studied in laboratories. However, despite the recent technological advancements, there has not been a valid in vivo method of evaluation involving clinical wear caused due to ceramics upon restored teeth and natural dentition. The aim of this paper is to review the latest advancements in all-ceramic materials, and their effect on the wear of opposing dentition. The descriptive review has been written after a thorough MEDLINE/PubMed search by the authors. It is imperative that clinicians are aware of recent advancements and that they should always consider the type of ceramic restorative materials used to maintain a stable occlusal relation. The ceramic restorations should be adequately finished and polished after the chair-side adjustment process of occlusal surfaces.

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).

Estudo comparativo in vitro da resistência ao desgaste entre o cimento de ionômero de vidro pó/líquido e o encapsulado

Resumo Introdução Os cimentos de ionômero de vidro possuem limitações devido à sua baixa resistência mecânica, a qual está diretamente relacionada com a proporção pó/líquido e a sua manipulação. Com o intuito de padronizar o proporcionamento e a manipulação, surgiram os cimentos de ionômero de vidro encapsulados, os quais possuem proporção pré-estabelecida e manipulação mecânica. Objetivo Comparar, in vitro, a resistência ao desgaste entre os cimentos de ionômero de vidro pó/líquido (Riva self cure e Riva light cure) e os encapsulados (Riva self cure e Riva light cure). Material e método As amostras foram divididas em quatro grupos, tendo sido confeccionados 48 corpos de prova (n=12), sendo 12 para cada grupo, com as seguintes dimensões: 7 mm de diâmetro e 4 mm de espessura. O desgaste foi avaliado de acordo com a massa perdida no processo de escovação (10.000 ciclos). Os valores obtidos na diferença entre a massa inicial e a massa final foram submetidos à análise de variância ANOVA e Teste de Tamhane (p<0,05). Resultado Segundo os resultados obtidos, todas as amostras sofreram perda de massa estatisticamente significativa e, em ordem crescente de desgaste, temos os cimentos de ionômero de vidro modificado por resina ‒ para os quais não houve diferença significativa entre o sistema pó/líquido (ΔM=11,62 mg e p=0,001) e o encapsulado (ΔM=12,96 mg e p=0,003) (p>0,05) ‒ seguidos pelo convencional pó/líquido (ΔM=20,68 mg e p=0,014) e o convencional encapsulado (ΔM=47,95 mg e p=0,002). Conclusão Pode-se conseguir uma resistência ao desgaste semelhante e até melhor no sistema pó/líquido.

Incorporation of CPP-ACP into Luting and Lining GIC: Influence on Wear Rate (in the Presence of Artificial Saliva) and Compressive Strength

The improvement of mechanical and antibacterial properties of glass ionomer cements (GICs) is an important goal in dental research. In this way, modification of GIC with caries preventive and remineralizing materials such as casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) is a new strategy to enhance its anticariogenic properties and the remineralization of teeth. However, one main concern is that adding CPP-ACP may have negative effects on the mechanical properties of GIC. This study investigated the influence of adding CPP-ACP on the wear rate (in the presence of artificial saliva) and compressive strength of luting and lining glass ionomer cement. CPP-ACP was incorporated into a luting and lining glass ionomer cement at different percentages (1, 1.56, and 2%). Wear rate and compressive strength were measured for each group using Pin-on-Disk tribometer device (in artificial saliva condition) and universal testing machine, respectively. The wear test was carried out in the presence of artificial saliva for better simulation of the oral environment. Our results demonstrated that increasing the percentage of CPP-ACP from 0 up to 1.56% (w/w), caused a decrease of 19% in the wear rate. However, at 2% (w/w) CPP-ACP, the wear rate increased. Compressive strength was improved by 31% when the CPP-ACP concentration was increased to 1.56% (w/w), but decreased when the concentration was raised to 2% (w/w). In conclusion, adding 1.56% CPP-ACP into luting and lining glass ionomer cement appears to provide an acceptable combination of two important mechanical properties, compressive strength and wear rate.

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.

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.

A study on the in-vitro wear of the natural tooth structure by opposing zirconia or dental porcelain

PURPOSE

This study was conducted to evaluate clinical validity of a zirconia full-coverage crown by comparing zirconia's wear capacity over antagonistic teeth with that of feldspathic dental porcelain.

MATERIALS AND METHODS

THE SUBJECT GROUPS WERE DIVIDED INTO THREE GROUPS: the polished feldspathic dental porcelain group (Group 1), the polished zirconia group (Group 2), and the polished zirconia with glazing group (Group 3). Twenty specimens were prepared from each group. Each procedure such as plasticity, condensation, and glazing was conducted according to the manufacturer's manual. A wear test was conducted with 240,000 chewing cycles using a dual-axis chewing simulator. The degree of wear of the antagonistic teeth was calculated by measuring the volume loss using a three-dimensional profiling system and ANSUR 3D software. The statistical significance of the measured degree of wear was tested with a significant level of 5% using one-way ANOVA and the Tukey test.

RESULTS

The degrees of wear of the antagonistic teeth were 0.119 ± 0.059 mm(3) in Group 1, 0.078 ± 0.063 mm(3) in Group 3, and 0.031 ± 0.033 mm(3) in Group 2. Statistical significance was found between Group 1 and Groups 2 and between Group 2 and 3, whereas no statistical significance was found between Group 1 and Group 3.

CONCLUSION

Despite the limitations of this study on the evaluation of antagonistic teeth wear, the degree of antagonistic tooth wear was less in zirconia than feldspathic dental porcelain, representing that the zirconia may be more beneficial in terms of antagonistic tooth wear.

Three-body wear of resin denture teeth with and without nanofillers

STATEMENT OF PROBLEM

The wear behavior of newly developed denture teeth with nanofillers may be different from teeth with other chemical formulations.

PURPOSE

The purpose of this study was to examine the 3-body wear resistance of 11 different commercially available resin denture teeth.

MATERIAL AND METHODS

The materials tested were conventional (SR Orthotyp PE, Orthognath) and cross-linked acrylic resin teeth without inorganic fillers (Premium 8, SR Postaris DCL, Trubyte Portrait, Artiplus), composite resin teeth with inorganic fillers (SR Orthosit PE, Vitapan), and composite resin teeth (experimental materials) with inorganic nanofillers (NC Veracia Posterior, e-Ha, Mondial). Human enamel and a ceramic denture tooth (Lumin Vacuum) were used as reference materials. The 3-body wear test was performed in a wear machine developed by the Academic Center for Dentistry Amsterdam (ACTA), with millet suspension acting as an abrasive medium (n=10, test load: 15 N, slip rate: 20%, number of cycles: 100,000). Wear was determined with the aid of a profilometer. Data were analyzed with the Kruskal-Wallis test and Mann-Whitney U test using the closed testing approach (significance level for familywise error rate, alpha=.05).

RESULTS

None of the acrylic and composite resin materials tested in this study demonstrated the 3-body wear resistance of ceramic teeth or human enamel. Teeth with inorganic fillers demonstrated significantly lower wear values than conventional or cross-linked acrylic resin teeth without fillers. Composite resin teeth with traditional fillers showed significantly lower wear than composite resin teeth with nanofillers.

CONCLUSIONS

Denture teeth with and without inorganic fillers differed significantly with regard to the degree of wear generated in the ACTA wear simulator. The incorporation of nanofillers did not improve the wear resistance compared to teeth with traditional fillers.

The abrasive effect of a porcelain and a nickel-chromium alloy on the wear of human enamel and the influence of a carbonated beverage on the rate of wear

PURPOSE

This study was conducted to determine the abrasive effect of a porcelain and an Ni-Cr alloy on the wear of human enamel, and the influence of a carbonated beverage on the rate of wear.

MATERIALS AND METHODS

Tooth specimens were prepared by embedding 48 freshly extracted mandibular first premolars in acrylic. Twenty-four of these specimens were abraded against Ni-Cr, and the remaining 24 against porcelain in artificial saliva and carbonated beverage media, respectively (n = 12), on a specially designed abrasive testing machine at a constant load of 40 N with 6 mm amplitude for 15,000 cycles. The cusp heights of the tooth specimens were measured both before and after abrasion using a profile projector. The abraded cast specimens were subjected to profilometry for computing the surface roughness; the abrading media was subjected to atomic absorption spectrophotometry for analyzing Ni and Cr ion levels. Data obtained were statistically analyzed.

RESULTS

Porcelain specimens in a medium of carbonated beverage caused the highest wear of tooth specimens. The lowest wear of tooth specimens was Ni-Cr specimens in artificial saliva medium. Carbonated beverage caused significantly higher wear of tooth specimens when abraded against Ni-Cr and porcelain specimens than did artificial saliva. The mean quantitative surface roughness of porcelain specimens was significantly higher than that of Ni-Cr specimens, irrespective of the medium in which abrasion testing was conducted. There was no statistically significant difference between the concentrations of Ni ions released in artificial saliva and carbonated beverage media. Also, there was no statistically significant difference between the concentrations of Cr ions released in artificial saliva and carbonated beverage media.

CONCLUSIONS

The wear of human enamel was significantly higher in the presence of carbonated beverage than artificial saliva and against porcelain when compared with Ni-Cr. The surface roughness of porcelain in the presence of carbonated beverage was found to be highest, and the release of Ni and Cr was not affected by carbonated beverage.

The impact of montmorillonite clay addition on the in vitro wear resistance of a glass-ionomer restorative

OBJECTIVES

The in vitro wear resistance of a glass-ionomer (GI) restorative ChemFil Superior (Dentsply DeTrey, Kanstanz, Germany) reinforced with either a pristine calcium montmorillonite (Ca-MMT) or an organically modified 12-amino-dodecanoicacid treated montmorillonite (ADA-MMT) clay was evaluated to investigate the potential of MMT reinforced GI restoratives as posterior filling materials.

METHODS

The wear resistance of a GI restorative reinforced with 0.5-2.5 wt.% Ca-MMT and ADA-MMT was assessed for groups of four disc-shaped specimens using the OHSU oral wear simulator operating at 20 N abrasion and 90 N attrition forces for 50,000 cycles at a frequency of 1 Hz in the presence of a poppy seed and PMMA micro-sphere slurry. The wear facet of each specimen was quantified by measuring the mean wear depth and mean volumetric wear in the abrasion (40-60% of wear facet) and attrition (80-90%) regions in conjunction with the mean total wear depth and mean total volumetric wear.

RESULTS

The addition of Ca-MMT clay resulted in a significant increase in the mean total volumetric wear and mean total wear depth of the GI restorative as the concentration of clay was increased utilising the one-way ANOVA and Tukey's test comparisons at a 95% significance level. When ADA-MMT clay was added to the GI no significant differences in mean total volumetric wear and mean total wear depth were evident (P<0.05).

CONCLUSIONS

The addition of Ca-MMT clay to the GI restorative resulted in a significant decrease in the in vitro wear resistance. ADA-MMT clay additions to the powder element of the GI restorative did not significantly enhance the in vitro wear resistance.

An evaluation of wear when enamel is opposed by various ceramic materials and gold

STATEMENT OF PROBLEM

Ceramic restorations have been known to cause wear of opposing enamel.

PURPOSE

The purpose of this study was to evaluate enamel wear caused by 3 ceramic substrates in the glazed and polished conditions.

MATERIAL AND METHODS

Sixty ceramic discs (10 x 2 mm)-20 each of Finesse, All-Ceram, and IPS-Empress-were prepared and glazed. Each group of 20 was divided into 2 groups of 10. The surfaces of one group were ground and polished using a porcelain polishing kit (Dialite). The remaining 10 were left as glazed. Ten specimens of a type III gold alloy were cast into rectangular shapes of 10 x 12 x 2 mm and polished. Seventy human cusps were prepared from sound, caries-free, extracted teeth and abraded against the substrates in a wear machine for a total of 10,000 cycles. The cusp height loss was traced before and after the wear test using a profile projector. Mean surface roughness (R(a)) values for the substrates were also recorded with a profilometer before testing. Differences in R(a) were evaluated using 1- and 2-way ANOVA and the Scheffe post hoc test (alpha = .05).

RESULTS

One-way ANOVA indicated that enamel height loss was significantly different by material (P < .001) and surface condition (glazed and polished or glazed; P < .05). Gold, polished Finesse, and polished All-Ceram were the least abrasive, whereas glazed IPS-Empress was the most abrasive. There was no significant interaction effect between substrate type and surface condition. Significant differences were found when R(a) of the substrate condition was compared with enamel wear (P < .01).

CONCLUSIONS

Gold, polished Finesse, and polished All-Ceram caused the least enamel wear, whereas IPS-Empress caused the most wear. Cast gold was significantly different than glazed IPS-Empress (P < .05), whereas other groups overlapped. There was significant correlation between R(a) and enamel wear (P < .01).

Wear of resin denture teeth by two-body contact

OBJECTIVES

The objective of this study was to examine the two-body wear resistance of nine different resin denture teeth and one experimental material.

METHODS

The two-body wear test was performed in a chewing simulator with an antagonistic Al(2)O(3) ball under an axial load of 40 N for 100,000 cycles. In each test series, an enamel sample was included as a reference. The wear was determined with an optical 3D surface profilometer. For statistical evaluation, SPSS for Windows was used.

RESULTS

The samples of Artiplus (18.7-SD 21.0) and e-Ha (21.2-SD 15.1) showed the lowest volumetric wear (in mm(3)x10(-3)) after 100,000 cycles. The difference from the other materials tested, except NC Veracia Posterior, was statistically significant (p=0.001-0.037). SR-Postaris-DCL (55.0-SD 6.8), SR-Orthosit-PE (61.1-SD 12.4) and Vitapan (72.1-SD 15.9) exhibited medium-sized wear values with low dispersion, whereas Orthognat (80.1-SD 31.6), Premium 8 (84.6-SD 31.4), NC Veracia Posterior (87.0-SD 52.7), SR-Orthotyp-PE (114.6-SD 28.0) and Trubyte Portrait (123.0-SD 45.6) showed high wear values with great variations. Statistically provable differences were found between SR-Orthotyp-PE and SR-Postaris-DCL (p=0.019) and also between SR-Orthotyp-PE and SR-Orthosit-PE (p=0.031). For enamel, a medium-sized wear value of 66.1-SD 76.8 was determined.

SIGNIFICANCE

The denture teeth examined showed differences in two-body wear resistance. The wear values determined were in some cases higher and in others lower than those of natural enamel. A definite connection between the wear resistance and the chemical composition of the materials could not be found in this investigation.

Textural characterization of finished and polished composites over time of intraoral exposure

This in situ study sought to evaluate the surface roughness evolution of resin composites finished and polished by different methods. A total of 108 rectangular-shaped specimens of a microfilled and a hybrid composite were cured against a Mylar matrix strip and left unpolished or instrumented with diamond burs, Al2O3-coated disks, Al2O3-impregnated UDMA disk, or with diamond burs followed by either one of the disks. After specimens had been profiled for the average surface roughness (Ra, microm), 18 volunteers wore a removable palatal appliance, which accommodated one specimen of each one of the 12 groups investigated. Surface roughness for up to 28 days of intraoral exposure was then measured at 1- or 7-day intervals. A split-plot ANOVA (alpha = 0.05) revealed a significant interaction between group and time. Tukey's test and regression analyses ascertained that initially finishing with burs only provided the roughest surface to both composites. Unpolished surfaces and those specimens polished with Al2O3-coated disks, regardless of previous use of diamond burs, attained smoother surface. The Al2O3-impregnated UDMA disk was capable of smoothening the surface of the hybrid material previously finished with diamond burs. The roughness achieved after finishing and polishing composites may be either smoothened or roughened after intraoral exposure. On the basis of the roughness range, it is advisable to use Al2O3-coated disks, regardless of whether diamond burs were previously used. Al2O3-impregnated UDMA disks (with or without previous application of diamond burs) may be also suitable for instrumenting hybrid restoratives.

In vitro wear resistance of three types of composite resin denture teeth

STATEMENT OF PROBLEM

The wear resistance of artificial teeth is important to the life of the removable prosthesis for the edentulous patient. The ability of artificial teeth to maintain a stable occlusal relationship over time may be influenced by this property.

PURPOSE

The purpose of this in vitro study was to evaluate the wear resistance of artificial teeth based on composite resin filler content when opposed by a denture tooth antagonist.

MATERIAL AND METHODS

The right first molars (both maxillary and mandibular) of 3 composite resin denture teeth (Endura, 47% organic filler; Duradent, 42% organic and inorganic filler; and Duracross, 68% organic filler) were secured in an in vitro 2-body wear-testing apparatus that simulated masticatory function (60 strokes/min, grinding distance of 2 mm, under 37 degrees C flowing water). Wear resistance was assessed as volume loss (mm3) and height loss (mm) at 5 kgf (grinding force) after 50,000 strokes (6 pairs for each type). The Vickers microhardness (VHN) of the occlusal surfaces was measured with a load of 50 g and a loading time of 30 seconds. After testing, the worn surfaces were observed with a scanning electron microscope (SEM). Mean values were analyzed using a 1-way analysis of variance followed by the Fisher test (alpha=.05).

RESULTS

The volume loss of Duradent teeth (0.87 +/- 0.03 mm3) was significantly higher than of the 2 other types of teeth tested (P<.001). The Duracross teeth (0.22 +/- 0.08 mm3 and 0.11 +/- 0.04 mm) exhibited the best wear resistance of the denture teeth tested. The wear resistance of the materials tested was consistent with their hardness (Endura 27.54 +/- 0.67 VHN, Duradent 24.00 +/- 0.60 VHN, Duracross 39.64 +/- 3.11 VHN). SEM observation showed that many filler particles were missing from the matrix of Duradent.

CONCLUSION

The wear resistance among the 3 types of teeth was significantly different; Duracross and Endura were more wear resistant than Duradent. Although the densities as reported by the manufacturer were similar, hardness and microstructure were the primary factors affecting the wear resistance of artificial teeth. Hardness appears to correlate with wear resistance since the wear resistance of Duradent with a lower VHN of 24 was greater than the other 2 types of teeth with greater hardness.

Influence of pH environment on polymer based dental material properties

OBJECTIVE

This study aims to analyze the influence of different pH environments causing degradation to the properties of polymer based materials.

DATA AND SOURCES

Studies were identified by searching published material in medical and dental literature using general and specialist databases, hand searching key dental journals and searching abstracts from conference proceedings.

STUDY SELECTION

Evaluation of published laboratory studies regarding the effects of different pH mediums on resin-based material properties.

CONCLUSION

For laboratory studies, slightly low pH mediums are the ones of choice to best mimic some in vivo conditions, but the effect seems to be slow acting. If the purpose is to accelerate dental composite hydrolysis and produce quick micro-structural damage to evaluate in vitro mechanical performances, suitable alternatives would be the use of high alkaline or very low acidic mediums.

Biocompatibility of micro- and nano-particles in the colon. Part II

Pathological colonic tissues were investigated with an Environmental Scanning Electron Microscope technique to verify the presence of inorganic, non-biodegradable pollutants, i.e. micro- and nano-debris of exogenous origin, after debris in liver and kidney had been discovered. In all, 18 samples of colon tissues affected by cancer and Crohn's disease were evaluated and found in all the cases to contain micro- and nano-particles. Their chemistry, detected with an X-ray microprobe, indicated a heterogeneous nature, whereas the size of the particles was homogeneous. Three control samples of healthy, young, cadavers were analysed and showed the absence of debris within the normal, healthy colon mucosa. The study reveals the presence of particulate debris, generally considered as biocompatible, in pathological specimens of human colon. The findings suggest a possible link between the presence of such particles and the underlying pathology in the cases analysed.

In vitro contact wear of dental composites

OBJECTIVE

The aim of this study is to determine the in vitro two-body contact wear mechanisms of three medium filled composites and compare these with a highly filled composite previously investigated.

MATERIALS AND METHODS

Three commercial dental composites with filler mass fraction loading of 75-76% were evaluated. Two of the composites contained Ba-B-Al-silicate glass fillers and fumed silica with different particle sizes and distributions. One of these composites contained a fairly uniform distribution of filler particles ranging in size from 1 to 5 microm, whereas the particle size distribution in the second composite was bimodal consisting of small (less than 1 microm) and large (about 10 microm) particles. The third composite contained Ba-Al-silicate glass and silica with a filler particle size of approximately 1 microm. The composite disks were tested for wear against harder alumina counterfaces. Wear tests were conducted in distilled water using a pin-on-disk tribometer under conditions that represented typical oral conditions (sliding speed of 2.5 mm/s and contact loads ranging from 1 to 20 N). The wear tracks were analyzed by scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy to elucidate the wear mechanisms. The chemical composition of the water solution collected after the tests was determined using an inductively coupled plasma-mass spectrometer (ICP-MS) to detect possible chemical changes, e.g. dissolution of trace elements due to submersion or wear. The wear results were compared with those reported in an earlier study on a highly filled composite containing predominately alumino-silicate glass fillers and alumina at a filler loading of 92%.

RESULTS

The differences in two-body wear rates between the three medium filled composites were not statistically significant (p<0.05) indicating that the variations in filler particle size and slight differences in chemical composition of the glass fillers do not affect the in vitro wear rates of these composites. Wear rates of these medium filled composites, however, were significantly lower than the highly filled composite (p<0.05). SEM, FTIR and ICP-MS analyses suggested that wear in the medium filled composites occurs by a complex set of processes involving tribochemical reactions between filler particles and water, formation of surface films containing a mixture of filler fragments and reaction products, and film delamination, as well as dissolution of the reaction products.

SIGNIFICANCE

This study reveals that subtle changes in the filler particle size and small differences in filler composition do not significantly affect the two-body wear behavior of medium filled composites. However, the chemistry of filler particles plays an important role in altering the wear performance of composites when significant changes are made in the chemical composition of the fillers and when the filler loading is increased.

Comparative study of the surface roughness of Ormocer-based and conventional composites

The aim of this study was to evaluate the surface roughness of two Ormocer-based resin composites before and after mechanical toothbrushing. The study compared the brands Admira and Definite with composites based on conventional monomer systems (Bis-GMA, Bis-EMA, UEDMA e TEGDMA), Z250 and A110. Eight samples of each material with 4mm in diameter and 2mm in height were prepared using a metallic mold. After 24 hours they were polished and examined with a profilometer for measurement of the initial surface roughness (Ra, mm) before mechanical toothbrushing (30,000 cycles). After toothbrushing, the samples were taken to the profilometer once again to check the final surface roughness. The results were submitted to ANOVA and Tukey test (5%). The Admira composite presented a higher mean of surface roughness before toothbrushing (0.132mm), with a statistical difference from the composite A110 (0.082mm). Definite (0.110mm) and Z250 (0.105mm) composites showed no differences between themselves or among the other composites. No statistical differences were observed after toothbrushing between the composites Definite (0.178mm), Z250 (0.187mm), Admira (0.181mm), and A110 (0.193mm). All composites showed a statistically significant increase in the surface roughness after toothbrushing.

The comparison of wear characteristics of prosthodontic restorative materials

AIM

To assess the mutual wear characteristics of various prosthodontic restorative materials.

MATERIALS AND METHODS

Samples were prepared using base metal alloy, ceramics and aesthetic methyl metacrylate resin materials in cylinders with a diameter of 30 mm, height 4 mm, and a spherical shape with a diameter of 5 mm and length of 6 mm. The mutual wearing process of samples on each other in groups was tested using a pin-on disc wear tester machine.

RESULTS

The data obtained were evaluated by means of variance analysis and T-test. It was determined that the percentages of the mutual wearing of the restorative materials were statistically significant (p<0.001), but whether the samples were in the upper or lower position had no statistical significance.

CONCLUSION

Various prosthodontic restorative materials had wear characteristics affecting each other.

Mechanical properties and microstructures of glass-ionomer cements

OBJECTIVE

The objective of this study was to determine the flexural strength (FS), compressive strength (CS), diametral tensile strength (DTS), Knoop hardness (KHN) and wear resistance of ten commercial glass-ionomer cements (GICs). The fracture surfaces of these cements were examined using scanning electron microscopic (SEM) techniques to ascertain relationships between the mechanical properties and microstructures of these cements.

METHODS

Specimens were fabricated according to the instructions from each manufacturer. The FS, CS, DTS, KHN and wear rate were measured after conditioning the specimens for 7 d in distilled water at 37 degrees C. One-way analysis of variance with the post hoc Tukey-Kramer multiple range test was used to determine which specimen groups were significantly different for each test. The fracture surface of one representative specimen of each GIC from the FS tests was examined using a scanning electron microscope.

RESULTS

The resin-modified GICs (RM GICs) exhibited much higher FS and DTS, not generally higher CS, often lower Knoop hardness and generally lower wear resistance, compared to the conventional GICs (C GICs). Vitremer (3M) had the highest values of FS and DTS; Fuji II LC (GC International) and Ketac-Molar (ESPE) had the highest CS; Ketac-Fil (ESPE) had the highest KHN. Ketac-Bond (ESPE) had the lowest FS; alpha-Silver (DMG-Hamburg) had the lowest CS. Four GICs (alpha-Fil (DMG-Hamburg), alpha-Silver, Ketac-Bond and Fuji II) had the lowest values of DTS, which were not significantly different from each other; alpha-Silver and Ketac-Silver had the lowest values of KHN. The highest wear resistance was exhibited by alpha-Silver and Ketac-Fil; F2LC had the lowest wear resistance. The C GICs exhibited brittle behavior, whereas the RM GICs underwent substantial plastic deformation in compression. The more integrated the microstructure, the higher were the FS and DTS. Higher CS was correlated with smaller glass particles, and higher KHN was found where there was a combination of smaller glass particles and lower porosity. Larger glass particle sizes and a more integrated microstructure contributed to a higher wear resistance.

SIGNIFICANCE

The mechanical properties of GICs were closely related to their microstructures. Factors such as the integrity of the interface between the glass particles and the polymer matrix, the particle size, and the number and size of voids have important roles in determining the mechanical properties.

Comparison of the abrasive wear resistance between amalgams, hybrid composite material and different dental cements

This paper reports on the abrasion wear of various restorative dental materials (three amalgams and two dental cements and a hybrid composite material) commonly used in dentistry. The mechanical properties, surface roughness and the volume loss by abrasion were determined for the different materials studied. The results showed a better profile for the amalgams versus the composite materials due to the failure of the polymeric matrix of the latter materials. However, the amalgams exhibited corrosion observed by means of Scanning Electron Microscopy.

Three-body wear associated with three ceramics and enamel

STATEMENT OF PROBLEM

Wear of human enamel is a clinical concern whenever opposing teeth need to be restored using ceramic restorations.

PURPOSE

This in vitro study investigated wear of human enamel and 3 dental ceramics: a conventional porcelain (Vitadur Alpha), a low-fusing hydrothermal ceramic (Duceram-LFC), and a machinable ceramic (Vita Mark II) in a 3-body wear test.

MATERIAL AND METHODS

Thirty pairs of tooth-ceramic specimens were tested in a dental wear machine, under a standard load (40 N), rate (80 cycles/minute), and for 25,000 cycles in a simulated food slurry medium. Amount of wear was determined by measuring the height loss of the tooth and depth of wear track of the ceramic materials. Analysis of variance (ANOVA) was used to analyze the data, followed by Bonferroni multiple comparisons method to produce sets of simultaneous 95% confidence intervals.

RESULTS

ANOVA revealed significant differences between the groups for both enamel wear (P =. 002) and ceramic wear (P <.001). Further comparisons (95% CI significance level) revealed that the difference in enamel wear produced by Alpha porcelain and Duceram-LFC ceramic material was not statistically significant, whereas that produced by Vita Mark II ceramic was significantly less. Vita Mark II ceramic was significantly more resistant to wear than Alpha porcelain and Duceram-LFC ceramic. Furthermore, Alpha porcelain was significantly more resistant to wear than Duceram-LFC ceramic.

CONCLUSION

The abrasiveness of Alpha porcelain and Duceram-LFC ceramic was similar, yet both were significantly more abrasive than Vita Mark II ceramic. In addition, Vita Mark II was the most wear-resistant ceramic and Duceram-LFC ceramic the least resistant.

Programmed occlusal reconstruction in anticipation of tooth wear

A procedure is presented that developed posterior lateral contacts in group function, despite existence of an anterior canine disclusion. This procedure allows a smooth transition into group function as the canine is subjected to natural attrition.

Wear of low-fusing dental porcelains

STATEMENT OF PROBLEM

The resistance of wear of dental porcelains is of concern when selecting a material for metal-ceramic and all-ceramic restorations.

PURPOSE

An in vitro investigation was performed to rank a number of dental porcelains with respect to their wear-resistance properties. Material and methods. The wear test of 9 dentin porcelains was carried out on a wear test machine and the amount of wear was measured as the reduction of height of the specimens. The surface hardness and surface roughness were also considered.

RESULTS

Resistance of wear was lowest for Finesse porcelain, and highest for Creation porcelain. Surface hardness values of the porcelain were quite similar for all porcelains but could be classified into 3 groups with Finesses and Vita Alpha porcelains as the softest and Creation porcelain as the hardest material.

CONCLUSIONS

The low-fusing porcelain Finesse showed less abrasion resistance in comparison with Ducera Gold and Ti-Ceram porcelains. Among the high-fusing types, Vita Alpha porcelain was more wear-disposed than the others.

Evaluation of wear of selected prosthetic materials in contact with enamel and dentin

STATEMENT OF PROBLEM

The proper choice of prosthetic materials for restoration of occlusal surfaces is important for the protection of the hard tissue of the opposing teeth and for regular functioning of the stomatognathic system.

PURPOSE

This study evaluated the resistance to wear of gold, Palliag M, Dentacolor, Chromasit, and Stellon materials and the enamel and dentin of natural teeth during functional contacts in an artificial oral environment with and without an abrasion material (Al2 O3 ).

MATERIAL AND METHODS

The 5 nonceramic prosthetic materials used in the restoration of occlusal surfaces of fixed partial dentures were examined in contact with enamel and dentin during a simulated masticatory process in 2 environments (with and without abrasion). Wear was evaluated by means of a special device designed for wear examination.

RESULTS

The findings highlighted that the wear of nonceramic prosthetic materials in contact with enamel or dentin was similar. Dentin showed greater wear when in contact with these materials than with the enamel surface.

CONCLUSION

Artificial environmental factors significantly influenced the wear of the hard tissue of teeth, especially when in contact with materials having low microhardness.

In vitro investigation of the wear of human enamel by dental porcelain

STATEMENT OF PROBLEM

Metal ceramic systems are advocated when both esthetics and strength are required. A major drawback to many porcelains is their wear and destruction of opposing natural dentition.

PURPOSE

This study evaluated the wear of enamel opposing 1 traditional and 2 recently introduced low-fusing feldspathic dental porcelains.

MATERIAL AND METHODS

Six blocks of Ceramco II, Finesse, and Omega 900 feldspathic porcelain materials were fabricated and fired according to manufacturer recommendations. Porcelain blocks were polished through 0.25 microm diamond polishing paste. Thirty-six enamel specimens were obtained and milled to a 2 mm (+0.5 mm) diameter. Enamel specimens were attached to an offset cam motor operating at 60 Hz. Enamel specimens were in constant contact with the stationary porcelain blocks under a load of 600 g and traversed a distance of 8 mm. Diameter and height of enamel specimens were measured at times of 0, 6, 12, 24, and 48 hours and subsequent determination of enamel volume loss recorded. Profilometric surface roughness of the ceramic blocks was also measured for the corresponding times.

RESULTS

Statistical analysis revealed that both Finesse and Omega 900 feldspathic porcelains caused significantly less enamel volume loss when compared with Ceramco II porcelain at all time intervals. Surface roughness revealed no consistent significant differences among porcelains.

CONCLUSION

Both Finesse and Omega 900 porcelains were not as destructive to human tooth structure as Ceramco II porcelain. These results suggest an advantage of the new, lower-fusing porcelains in conditions where natural dentition wear is a concern.

Considerations when planning occlusal rehabilitation: a review of the literature

As one of the most demanding tasks facing the restorative dentist, planning and executing an occlusal rehabilitation should not be undertaken lightly. The stakes are high and failure is costly. Treatment planning decisions should be undertaken on the basis of scientific evidence, where this is available, or on the basis of documented experience where it is not. This review article identifies the major biological and clinical considerations used when planning an occlusal rehabilitation. These include the indications for reorganising the occlusion, the choice of condylar position and occlusal scheme, the implications of and indications for increasing the vertical dimension, replacing missing teeth and the choice of materials. Finally, the literature surrounding the controversial issue of occlusal rehabilitation as a means to treat temporo-mandibular disorders is also reviewed.

Investigation of human enamel wear against four dental ceramics and gold

OBJECTIVES

This in vitro study compared the wear of enamel against aluminous porcelin, bonded porcelain, low fusing hydrothermal ceramic, feldspathic machinable ceramic, and cast gold.

METHODS

Fifty pairs of tooth-material specimens were tested in a dental wear machine, under a standard load (40 N), rate (80 cycles min-1) and for 25,000 cycles in distilled water. The amount of wear was determined by measuring the height loss of the tooth, and the depth of wear track of the restorative materials.

RESULTS

There was a significant difference in wear among the groups for both enamel and materials (p < 0.001). Follow-up comparisons (95% CI significance level) showed that gold caused significantly less enamel wear than all ceramics tested. The amount of enamel wear in the aluminous and bonded porcelain groups was significantly higher than with the hydrothermal and machinable ceramic groups. There was no significant difference between the amount of enamel wear produced by the aluminous and bonded porcelains nor between that produced by the hydrothermal and machinable ceramics. Furthermore, the wear of the aluminous and bonded porcelains was significantly greater than that of the hydrothermal ceramic, the machinable ceramics and gold. No significant difference in wear was found between aluminous and bonded porcelains, hydrothermal and machinable ceramics, or between machinable ceramic and gold. However, the hydrothermal ceramic had significantly greater wear than gold.

CONCLUSIONS

It was concluded that the hydrothermal and the machinable ceramics were significantly less abrasive and more resistant to wear than the conventional aluminous and bonded porcelains. Gold was the least abrasive material and most resistant to wear, although the difference in wear between the machinable ceramic and gold was not statistically significant.

Clinical wear study of three commercially available artificial tooth materials: thirty-six month results

STATEMENT OF PROBLEM

Excessive wear of artificial resin teeth has been a concern to both the patient and the dentist because of unfavorable associated sequelae. The search for a more wear resistant resin tooth material resulted in the development of modified resin teeth that displayed acceptable wear resistance.

PURPOSE

This study compared clinical wear of a new modified resin tooth material with two other commercially available modified resin materials over a period of 36 months. Differences in wear by gender, cuspal anatomy, arch, individual tooth type, and chewing side preference were also evaluated.

MATERIAL AND METHODS

A total of 67 patients were randomized into one of three treatment groups in this double-blind study; group 1, Ivoclar-Vivodent and Orthotyp; group 2, Dentsply-Trublend SLM; and group 3, Dentsply-Bioblend IPN. Tooth wear was determined by measuring vertical heights of contacting points at baseline and 36 months with a computerized coordinate measuring machine and computer-controlled positioning stages. Measurements were completed at 36 months for 55 patients who remained in the study.

RESULTS

Repeated measures analysis of variance revealed no significant difference in total wear by gender or tooth material at 36 months. There was also no significant difference by chewing side preference or cuspal anatomy. However, there was a significant difference in individual tooth wear (canine, premolar, molar) and by arch.

CONCLUSION

New modified resin teeth have displayed clinically acceptable wear resistance for most patients.

Proximal wear rates by tooth position of resin composite restorations

OBJECTIVE

The purpose of this study was to evaluate restorations, previously placed in clinical trials, for the rate of wear of the proximal surfaces, by tooth position.

MATERIALS AND METHODS

Seventy resin composite restorations were evaluated in bicuspids and molars. Fifty restorations were direct placement restorations and 20 were indirect placement restorations. Thirty-five bicuspids and 35 molars were evaluated for proximal wear rate. All restorations were opposing unrestored enamel proximal surfaces. Ten enamel to enamel proximal surfaces were chosen as controls. At baseline, contacts were judged to be closed visually and with thin, unwaxed dental floss. Impressions were taken at baseline and after 6, 12 and 24 months for the fabrication of models. Measurements for proximal wear, as determined by a loss of space between indexed transfer copings, were made under a zoom stereomicroscope by two independent evaluators. A parametric ANOVA, Student-Newman-Keuls, and log curve fit were applied to the data.

RESULTS

When all data were pooled regardless of material, there were no significant differences (P < 0.05) in wear values for 1st and 2nd bicuspids and 1st and 2nd molars. Wear rates showed a high correlation (log curve fit R2 > 0.950) regardless of actual amount of wear.

CONCLUSIONS

Regardless of composites examined, there were no differences in the amount of proximal wear with regard to tooth position in the arch.