Stepwise stress testing of different CAD-CAM lithium disilicate veneer application methods applied to lithium disilicate substructures.

STATEMENT OF PROBLEM: Whether a computer-aided design and computer-aided manufacture (CAD-CAM) fabricated high-translucency lithium disilicate veneer on a lithium disilicate substructure would increase the strength of the restoration compared with a traditional feldspathic porcelain veneer is unclear. PURPOSE: The purpose of this in vitro study was to evaluate the effect of different lithium disilicate veneer application methods on a lithium disilicate substructure on their biaxial flexural stress (BFS). MATERIAL AND METHODS: Lithium disilicate disks were fabricated so that when combined with the veneering disks, they had a dimension of 12×1.2 mm. Experimental groups were as follows (n=15): resin-bonded lithium disilicate veneer, lithium disilicate veneer adhesively cemented to lithium disilicate; sintered lithium disilicate veneer, lithium disilicate veneer sintered to lithium disilicate; sintered feldspathic veneer, feldspathic porcelain applied to lithium disilicate; and monolithic lithium disilicate, the control group. Weibull distribution survival analysis was used to compare the differences in the resistance to fracture after fatigue. The total number of cycles was analyzed by using 1-way ANOVA (α=.05). A finite element analysis (FEA) was also performed. The maximum principal stress (MPS) was used as the failure criterion. RESULTS: The sintered feldspathic veneer group had significantly lower fatigue resistance than sintered lithium disilicate veneer or resin-bonded lithium disilicate veneer (P<.05). The resin-bonded lithium disilicate veneer group showed significantly more fractured fragments than the other groups. No statistical difference was observed in the number of cycles. The lithium disilicate veneered groups presented similar resistance to fatigue as the monolithic specimens of the same overall dimensions. Higher peaks of MPS were observed for groups monolithic lithium disilicate, sintered lithium disilicate veneer, and sintered feldspathic veneer than for resin-bonded lithium disilicate veneer. CONCLUSIONS: Veneering a lithium disilicate substructure with a lithium disilicate veneer, bonded or sintered, increased resistance to fatigue compared with a feldspathic porcelain veneer. The lithium disilicate veneer groups had similar fatigue resistance to that of the monolithic group.

Monitoring of simulated occlusal tooth wear by objective outcome measures.

OBJECTIVES: This in vitro study explored quantitative outcome measures as clinical indicators of simulated occlusal tooth wear progression. METHODS: Ten sound, extracted human premolars were selected and submitted to occlusal tooth wear simulation in 0.5-mm steps (0/0.5/1.0/1.5 mm). At each step, enamel thickness on the buccal cusp tips was evaluated using cross-polarization optical coherence tomography (CP-OCT) and micro-computed tomography (µ-CT). The occlusal surface of each premolar was also scanned at each step using a 3D digital intraoral scanner, followed by morphological characterization using standard topography attributes (Slope, Relief, RFI, OPCr). Repeated measures ANOVA assessed differences in simulated wear levels for the µ-CT and CP-OCT data as well as the topography values. Correlations were also calculated between the µ-CT/CP-OCT and topography data. RESULTS: Significant differences were observed for enamel thickness at each simulation wear stage, for both CP-OCT (p < 0.001) and µ-CT (p < 0.001), with good agreement between methods (intraclass correlation: 0.89). For topography analysis, as wear increased, the average Slope, RFI, and Relief values decreased, and average OPCr values increased, with more significant differences shown for Slope. Slope showed significant (p < 0.05) positive correlations with CP-OCT. OPCr showed significant negative correlations with µ-CT, and CP-OCT (p < 0.05). RFI and Relief were not correlated with either µ-CT or CP-OCT (p > 0.05). CONCLUSIONS: Our findings suggest the potential of PS-OCT for measuring enamel thickness changes in the cusp tips of the occlusal surface. Similarly, conventional intraoral scanners can serve effectively for monitoring overall tooth wear when combined with dental topographic analyses of resultant point clouds. CLINICAL SIGNIFICANCE: CP-OCT measures of enamel thickness and dental 3D topographic attributes showed potential as objective outcomes for the clinical monitoring of occlusal tooth wear. Their combination provided a comprehensive understanding of the tooth wear development process.

Clinical evaluation of a universal adhesive in non-carious cervical lesions.

OBJECTIVES: To compare the clinical performance of a universal adhesive in class V non-carious cervical lesions (NCCLs) using two surface treatment protocols (self-etch [SfE] vs selective-enamel-etch [SelE]). MATERIAL AND METHODS: Thirty-three adults, each with ≥2 NCCLs, received one resin composite restoration utilizing a SfE universal adhesive and another utilizing the adhesive and SelE with 37% phosphoric acid. Restorations were evaluated for sensitivity, retention, marginal discoloration, marginal adaptation, and clinical acceptability through 24 months using Cochran-Mantel-Haenszel tests for stratified, ordered categorical outcomes. RESULTS: Sixty-six restorations (35 SfE, 31 SelE; 27 volunteers) were evaluated at 24 months. There were no significant differences between SfE and SelE for sensitivity, retention, marginal adaptation, or clinical acceptability. One SfE restoration was lost. Marginal adaptation was significantly worse at 24 months than baseline for SelE (P = 0.01), but not for SfE. Marginal discoloration was significantly worse for SfE (P = 0.02), but not for SelE. Sensitivity improved from baseline to 24 months for both groups (SelE P = 0.004, SfE P = 0.002). CONCLUSIONS: Twenty-four-month data indicated significantly reduced sensitivity for both groups, worse marginal discoloration for SfE, and worse marginal adaptation for SelE. No changes in retention or clinical acceptability were observed in either group. All retained restorations were clinically acceptable at 24 months. CLINICAL SIGNIFICANCE: Both self-etch and selective enamel etch techniques with a universal adhesive produced clinically acceptable results in resin composite restorations for NCCLs over 2 years.

Retrospective assessment of caries experience among US Naval Academy midshipmen.

OBJECTIVE: To assess the 4-year caries incidence among US Naval Academy midshipmen. METHODS: Dental records (n = 300) from a total population of 1,016 midshipmen from the 2011 graduating class at US Naval Academy, Annapolis, MD, were randomly selected for review. Patients were assigned a caries risk status based on the number of caries lesions recorded at initial examination (low = 0 lesions; moderate = 1-2 lesions; high = 3+ lesions). For each risk category, caries prevalence (DMFS, DMFT) and caries incidence were calculated based on findings recorded at the initial (E1), third year (E2), and fourth year (E3) examinations. The most significant predictors for caries incidence were determined for each risk category. RESULTS: Mean DMFS and DMFT were significantly different for each risk group at each examination (low < moderate < high; one-way ANOVA, P < 0.05). Within each caries risk category, mean DMFS and DMFT increased significantly from E1 to E3 (repeated measures ANOVA, all P < 0.05). Compared with low-risk patients, total caries incidence was over 2× greater for moderate-risk and nearly 4× greater for high-risk patients (one-way ANOVA, P < 0.05). "Filled surfaces" was the most significant predictor for caries incidence among low-risk patients; among high-risk and all risk groups combined, the most significant predictors were "decayed surfaces" and "decayed surfaces plus incipient surfaces" (linear regression; all P < 0.047). CONCLUSIONS: Caries experience was consistently greater for moderate- and high-risk patients at all examinations. The magnitude of increase in caries experience was greater for moderate- and high-risk patients. Caries history and current disease status reliably predict future caries experience in this young adult population.

An evaluation of U.S. Navy Dental Corps classification guidelines.

OBJECTIVES: The aims of this research were to evaluate the effectiveness of two different sets of dental classification guidelines to differentiate dental emergency (DE) rates between deployable and nondeployable personnel. METHODS: A retrospective study of the dental records of two cohorts of Marine Corps recruits examined and treated using different classification guidelines was completed. RESULTS: Both classification systems showed significant differences between DE rates of nondeployable and deployable personnel. No statistical difference was observed when comparing the adjusted HRs of the two cohorts. CONCLUSIONS: Results of this study suggest that both guidelines are able to distinguish between deployable and nondeployable personnel and give reasonable assurance that class 1 and 2 patients will not experience a DE for a 6-month period. Incorporating factors such as caries risk, number of missing and filled teeth, and number of third molars may improve the ability of the dental classification systems in predicting DE.

An evaluation of replacement rates for posterior resin-based composite and amalgam restorations in U.S. Navy and marine corps recruits.

BACKGROUND: Restoration replacement is a clinical concern that has not been studied among military personnel. The authors determined the prevalence of placement of posterior amalgam and resin-based composite restorations and the incidence of replacement among U.S. Navy and Marine Corps personnel. METHODS: The authors analyzed dental records from 2,780 personnel to determine the relative risk of replacement for initially sound restorations during subjects' first years of military service. RESULTS: At the initial examination, 964 (15.2 percent) of amalgam restorations and 199 (17.4 percent) of resin-based composite restorations required re-treatment. Of those judged clinically acceptable, 14.2 percent of amalgam and 16.7 percent of resin-based composite restorations required replacement during the observation period. The authors found significant increases in replacement rates for resin-based composite restorations compared with amalgam restorations for replacement due to all causes (adjusted hazard ratio, 1.28; P < .05), as well as for replacement due to restoration failure (adjusted hazard ratio, 1.64; P < .01). CONCLUSIONS: About 30 percent of posterior restorations required replacement, either at the initial examination or during the subjects' first years of military service. In a young military population, significantly more resin-based composite restorations in place at the initial examination will require replacement than will amalgam restorations. Multi-surface restorations had higher rates of replacement than did one-surface restorations, and subjects at high caries risk experienced significantly higher replacement rates than did those at low caries risk. CLINICAL IMPLICATIONS: The number of surfaces restored and subjects' caries risk status may influence the longevity of resin-based composite and amalgam restorations.

Caries remineralization therapy: implications for dental readiness.

Caries remineralization therapy can effectively arrest or reverse the progression of incipient proximal caries lesions. Remineralization of tooth structure is accomplished via a series of topical fluoride applications over time using a combination of both in-office and at-home fluoride agents. Remineralization therapy should be considered a viable noninvasive alternative to restoration for all caries lesions that do not exhibit frank cavitation of the proximal enamel surface (i.e., all lesions in enamel, as well as most lesions in the outer dentin). Combining a conservative restorative approach with an aggressive caries remineralization program may provide substantial therapeutic benefit and significantly reduce both costs and long-term restorative need among military patient populations.

A statistical method to evaluate dental classification systems used by military dental services.

UNLABELLED: The aim of this research project was to develop a systematic approach to evaluate the effectiveness of dental classifications used by military dental services to predict dental emergencies. DESIGN: A retrospective cohort study of U.S. Navy recruits were followed for an average of 3.5 years. Dental records of 1,114 recruits who had their initial dental examination during the calendar year 1997 were collected in 2001. Four hundred sixty-two dental emergencies (DE) were recorded, of which 50 were class 3 patients. The incidence density ratio (IDR) of DE was 2.2 (p < 0.001; class 3 compared to class 1 or 2 patients). The mean times to DE in patients who experienced DE were 92 days (class 3 patients) and 418 days (class 1 and 2 patients; p < 0.001), while the median times to DE were 59 days and 295 days (p < 0.001) for class 3 and class 1 or 2, respectively. The adjusted hazard ratio for DE in class 3 versus class 1 and 2 patients was 1.519 (p = 0.0149). We have concluded that examination of the following statistics is necessary to assess the effectiveness of military dental classification systems: (1) the percentage of DE that occur in class 3 patients, (2) the IDR of DE, (3) the mean time to DE, (4) the median time to DE, and (5) the hazard ratio of DE.

Periodontal health status in a cohort of young US Navy personnel.

OBJECTIVES: Neither the prevalence of periodontal disease nor long-term trends in periodontal health among US military personnel has been well studied. The authors analyzed dental records to assess the prevalence and severity of periodontal disease, characterize changes in periodontal health, and determine the associations of age, race, gender, and tobacco use with periodontal status among US Navy personnel. METHODS: Dental records from 1,107 personnel who entered military service in 1997 were gathered from eight US Navy dental treatment facilities. Demographic information, tobacco use status, and periodontal health status, as reflected by the Periodontal Screening and Recording (PSR) information recorded at each required dental examination during the 4-year observational period (1997 to 2001), were collected. To improve sensitivity in measuring the extent of periodontal disease, the standard five-point PSR scale was reexpressed as a "PSR grade." RESULTS: Over 98 percent of Navy recruits exhibited some level of periodontal disease at initial examination. Most (76 percent) exhibited gingivitis of varying severity. Over a mean observational period of 3.4 years, 91 percent of subjects received at least one oral prophylaxis, and over 60 percent received two to four prophylaxes. Subjects with severe periodontal conditions received as many as 22 appointments for prophylaxis or periodontal therapy. From initial to final examination, periodontal status improved for 29.2 percent of subjects, deteriorated for 31.3 percent, and remained unchanged for 39.5 percent. Subjects presenting initially with healthy periodontia, or gingivitis without evidence of periodontitis, tended to deteriorate or remain unchanged, while those exhibiting periodontitis tended to improve with periodontal therapy. Race (non-White) and greater age at entry were significantly associated with increased risk for poorer periodontal health at both initial and final examination. CONCLUSIONS: Although a needs-based dental care model appears effective in managing periodontal disease among those receiving active therapy, patients who receive sporadic care may deteriorate over time. To maintain periodontal health in this population, appropriate preventive and periodontal therapies should be provided soon after entry and repeated at intervals specific to individual patient need.

Effects of five thermal stressing regimens on the flexural and bond strengths of a hybrid resin composite.

UNLABELLED: Thermocycling is commonly employed in laboratory studies to simulate the in vivo aging of restorative materials. However, there is little consistency in the regimens used, and some researchers have questioned the clinical relevance and, hence, the necessity of including thermal stressing in in vitro protocols. This study examined the effects of five thermal stressing regimens on the flexural and dentin bond strengths of a hybrid resin composite. METHODS: For flexural strength tests, 95 rectangular specimens (15 mm x 2 mm x 2 mm) were fabricated using a stainless steel split mold, then light cured for 60 seconds. For bond strength tests, 75 caries-free molars were flattened occlusally to expose dentin, then polished through 600 grit SiC paper; dentin surfaces were etched, rinsed and blotted dry. A dentin adhesive was applied and light cured for 30 seconds; resin composite was condensed through a stainless steel split mold (4.3 mm diameter x 3.5 mm high), then light cured for 60 seconds. All specimens were stored in deionized water for 24 hours, then stressed for 100 hours according to one of five regimens: 1) cycled between 5 degrees C and 55 degrees C (9000 cycles; 20-second dwell time); 2) held at 5 degrees C constant; 3) held at 22 degrees C constant; 4) held at 55 degrees C constant; 5) held at 5 degrees C for 50 hours, then at 55 degrees C for 50 hours. Flexural strengths were measured using an Instron 5500R and three-point bending apparatus at a crosshead speed of 0.5 mm/minute. Shear bond strengths were measured using an MTS Bionix 200 at a crosshead speed of 0.5 mm/minute. RESULTS: ANOVA revealed no significant differences in either flexural strength or shear bond strength among the five thermal regimens.

Dental sealant longevity in a cohort of young U.S. naval personnel.

BACKGROUND: The U.S. Navy emphasizes caries prevention and encourages the placement of dental sealants on the caries-susceptible teeth of patients at risk of developing caries. The authors analyzed dental records to assess the longevity of dental sealants placed in naval personnel. METHODS: A cluster sample of dental records from 1,123 personnel who entered naval service in 1997 was drawn from eight Navy dental treatment facilities. The authors determined the number of sealants provided, the number of sealants that failed over the observation period (1997-2001), the dates of sealant failure and the longevity of sealants placed during and after recruit training. RESULTS: A total of 319 personnel received sealants during their first two years of service. The authors evaluated 1,467 sealed teeth. They followed the sealants for an average of 35 months. They noted 179 sealant failures in 102 subjects; 69 previously sealed teeth required sealant replacement, and 110 sealed teeth required restoration of the occlusal surface. Among those sealants that failed, the mean length of time from placement to failure was 26 months. Sealant failure rates were significantly higher among subjects at moderate risk or high risk of developing caries than among subjects at low risk. CONCLUSIONS: After an average of 35 months, 87.8 percent of the sealants placed in this population were retained and functional. Subjects who were at moderate or high risk of developing caries demonstrated significantly higher sealant failure rates than those at low risk of developing caries. CLINICAL IMPLICATIONS: Dental sealants can be retained successfully in adults. They should be considered a viable treatment alternative for adult patients who are susceptible to caries; however, patients at elevated risk of developing caries may require more frequent re-evaluation and maintenance to achieve maximum benefit.

Effect of three direct restorative materials on molar cuspal fracture resistance.

PURPOSE: This study compared the cusp fracture strength of molars restored using a condensable resin composite with that of teeth restored with conventional amalgam, a bonded amalgam, and an incrementally placed resin composite. METHODS: Standardized MOD cavity preparations (2/3 the buccal-lingual dimension x 4 mm deep) were made in 50 extracted human molars and restored as follows (n = 10): (1) a packable posterior resin composite; (2) an incrementally placed microfilled posterior resin composite; (3) a spherical particle amalgam alloy; (4) spherical amalgam with a dentin adhesive liner and (5) no restoration (preparation only; negative control). A sixth group of intact molars (n = 10) served as a positive control. Following storage and thermocycling, each specimen was tested for cuspal fracture strength. RESULTS: Cavity preparation reduced cuspal fracture strength by over 50%. The fracture strength of intact teeth was significantly greater than that of all other groups (P< 0.0001). None of the restorative procedures increased cuspal fracture resistance over that of prepared teeth.

Effects of daily fluoride exposures on fluoride release by glass ionomer-based restoratives.

It is well documented that glass ionomer cements absorb and release fluoride following single fluoride exposures. This study examined fluoride release among three glass ionomer-based restorative materials following multiple daily exposures to three topical fluoride regimens. Using a Delrin mold, 32 cylindrical specimens, each of a glass ionomer (Ketac-Fil), resin-modified glass ionomer (Photac-Fil) and polyacid-modified resin (Dyract AP) were created. Each specimen was subjected to one of four daily treatments (n = 8): (1) no fluoride treatment (control); (2) application of a fluoride dentifrice (1000 ppm) for one minute once daily; (3) application of the same dentifrice for one minute twice daily; (4) the same regimen as (3), plus immersion in a 0.05% sodium fluoride (NaF) mouth rinse (225 ppm) for one minute immediately following the second dentifrice application. Each specimen was suspended in a polyethylene test tube containing 1.0 ml demineralizing solution (pH 4.3) at 37 degrees C for six hours, then transferred to a new test tube containing 1.0 ml remineralizing solution (pH 7.0) at 37 degrees C for 18 hours. Fluoride treatments were completed at the time of transfer daily for seven days. Media solutions were buffered with equal volumes of TISAB II; fluoride levels were measured using a digital ion analyzer and fluoride electrode. Fluoride release decreased significantly from Day 1 to Day 3 for all materials regardless of fluoride treatment (Repeated Measures ANOVA, Tukey HSD, p < 0.05). All specimens released significantly more fluoride in demineralizing solution than in remineralizing solution. For Days 2-7, Treatment 4 produced greater fluoride release than both the control and Treatment 2 for all three materials (p < 0.05); For each material, the fluoride release produced by Treatments 3 and 4 was statistically similar on most days throughout the study. By Day 7, Photac-Fil demonstrated both the greatest total fluoride release and the greatest rechargability, followed by Ketac-Fil and Dyract AP. Although subsequent daily fluoride release never approached that of Day 1, increasing daily fluoride exposures enhanced fluoride release for all three restorative materials.

Light output of disposable vs. nondisposable curing light tips following high-level disinfection.

Following a pilot study which determined that autoclaving a disposable tip resulted in physical deformation, rendering the tip ineffective for photocuring, this study evaluated the effects of two FDA-cleared high-level disinfectants on the light output and physical integrity of disposable and nondisposable curing light tips. Nine disposable and five nondisposable curing tips were immersed in each of the two disinfectants. No significant differences (p > 0.05) in light output over time were observed for either type of curing light tip in either solution. None of the tips were physically affected by immersion and light output values remained in the acceptable range for resin composite polymerization.