A simple method to estimate restoration volume as a possible predictor for tooth fracture.

STATEMENT OF PROBLEM: Many dentists cite the fracture risk posed by a large existing restoration as a primary reason for their decision to place a full-coverage restoration. However, there is poor agreement among dentists as to when restoration placement is necessary because of the inability to make objective measurements of restoration size. PURPOSE: The purpose of this study was to compare a new method to estimate restoration volumes in posterior teeth with analytically determined volumes. MATERIAL AND METHODS: True restoration volume proportion (RVP) was determined for 96 melamine typodont teeth: 24 each of maxillary second premolar, mandibular second premolar, maxillary first molar, and mandibular first molar. Each group of 24 was subdivided into 3 groups to receive an O, MO, or MOD amalgam preparation design. Each preparation design was further subdivided into 4 groups of increasingly larger size. The density of amalgam used was calculated according to ANSI/ADA Specification 1. The teeth were weighed before and after restoration with amalgam. Restoration weight was calculated, and the density of amalgam was used to calculate restoration volume. A liquid pycnometer was used to calculate coronal volume after sectioning the anatomic crown from the root horizontally at the cementoenamel junction. True RVP was calculated by dividing restoration volume by coronal volume. An occlusal photograph and a bitewing radiograph were made of each restored tooth to provide 2 perpendicular views. Each image was digitized, and software was used to measure the percentage of the anatomic crown restored with amalgam. Estimated RVP was calculated by multiplying the percentage of the anatomic crown restored from the 2 views together. Pearson correlation coefficients were used to compare estimated RVP with true RVP. RESULTS: The Pearson correlation coefficient of true RVP with estimated RVP was 0.97 overall (P

Clinical evaluation of two one-bottle dentin adhesives at three years.

BACKGROUND: The method currently used to adhere resin to dentin involves etching, priming and bonding. Many commercial adhesives now combine priming and bonding functions in a single solution, and these are frequently called one-bottle adhesives. The purpose of this study was to compare the 36-month clinical performance of two commercial one-bottle adhesives. METHODS: The authors enrolled 33 patients with noncarious cervical lesions in the study. A total of 101 lesions were restored with either a filled, ethanol-based adhesive (OptiBond Solo, SDS Kerr) or an unfilled, acetone-based adhesive (Prime & Bond 2.1, Dentsply Caulk) and a hybrid resin-based composite. Enamel margins were not beveled, and no mechanical retention was placed. The restorations were evaluated at baseline and six months, 18 months and 36 months after placement using modified Cvar/Ryge criteria. RESULTS: The retention rates at 36 months were 93.3 percent for the ethanol-based adhesive and 89.4 percent for the acetone-based adhesive. The difference in retention rates was not statistically significant. In both groups, 12 percent of the retained restorations had marginal staining, but no recurrent caries was detected around any restoration. Other restoration characteristics such as marginal adaptation and color match remained excellent three years after placement. CONCLUSIONS: The performance of both adhesives was excellent during this 36-month clinical trial. At the most recent recall evaluation (that is, 36 months), the filled, ethanol-based adhesive exhibited slightly better bond durability, but the difference between the two materials was not statistically significant. CLINICAL IMPLICATIONS: The one-bottle adhesives evaluated in this study provided excellent clinical retention of Class V restorations without mechanical retention. When the materials are used properly, restorations are retained at a high rate during at least three years of clinical service.

Eighteen-month clinical evaluation of a filled and unfilled dentin adhesive.

OBJECTIVE: The purpose of this study was to evaluate the performance of a filled (OptiBond Solo) and an unfilled (Prime & Bond 2.1) "one-bottle" adhesive in Class V restorations after 18 months of clinical service. METHODS: Thirty-three patients with non-carious cervical lesions were enrolled in the study. A total of 101 lesions were restored using one of the adhesives and a hybrid composite resin. Enamel was not beveled, nor was any mechanical retention placed. The restorations were evaluated at baseline, and at 6 and 18 months after placement using modified USPHS criteria. RESULTS: Cumulative 18-month retention rates were 93.6% for OptiBond Solo and 98.0% for Prime & Bond 2.1. The difference in retention rates was not statistically significant. For OptiBond Solo, the only notable problems were interfacial staining and marginal adaptation, both of which were less than ideal in 9% of restorations. Marginal problems were slightly less frequent for Prime & Bond 2.1 restorations, but the difference was not significant. CONCLUSIONS: Both adhesives provided Class V retention rates exceeding the 18-month, full acceptance guidelines set by the American Dental Association. Any additional benefit provided by the use of a filled adhesive was not detected in this 18-month clinical trial.

Margin gap size of ceramic inlays using second-generation CAD/CAM equipment.

OBJECTIVE: The goal of this study was to determine if the fit of second-generation computer-assisted design/computer-assisted manufacturing (CAD/CAM) (CEREC 2, Sirona Dental Systems, Bensheim, Germany) inlays within Class II cavity preparations were within the range of 50 to 100 microns and were equal or better to CEREC 1 inlays. MATERIALS AND METHODS: Extracted human molars free of surface defects and caries were prepared with standard mesio-occlusodistal cavity preparations. Ceramic inlays were fabricated with CEREC 2 CAD/CAM equipment and seated into cavity preparations. Digital images were captured at 100 times magnification. Marginal gaps were measured with an image analysis program. For each restoration, gaps were measured at 12 locations along interproximal margins and 10 locations along occlusal margins. RESULTS: No difficulty occurred in seating any of the milled inlays. Average marginal gaps for occlusal (59 +/- 35 microns) and interproximal (97 +/- 66 microns) margins were statistically different (t-test, p < or = .01). Average marginal gap for all sites combined was 80 +/- 57 microns. Marginal gap widths were smaller than those obtained from a similar study done earlier with the CEREC 1 unit for occlusal (89 +/- 65 microns) and interproximal (105 +/- 81 microns) margins. Ease of seating with CEREC 2 inlays was much better than with CEREC 1. CLINICAL SIGNIFICANCE: Improvements in software and hardware allow the CEREC 2 to adapt well to standard inlay cavity preparations. The ability of the device to create inlays that seat without interference is remarkable. The improved fit and ability to create the occlusal surface in a variety of ways make CEREC 2 an attractive restorative option for all-ceramic restorations.

Effect of powder/liquid ratio on the clinical and laboratory performance of resin-modified glass-ionomers.

OBJECTIVES: To compare the effects of powder/liquid (P/L) ratio and surface wetness on retention of adhesive Class V restorations. METHODS: One-hundred and six Fuji II LC restorations were placed at two clinical trial sites. In the 'high-dry group (Site A), Fuji II LC was mixed at a P/L ratio of 3.0 and applied to dentine that was visibly dry, but not desiccated. In the 'low-wet' group (Site B), Fuji II LC was mixed at a P/L ratio of 2.25 and applied to dentine that was glisteningly moist. The restorations were evaluated at baseline, 1 and 2 years at both sites, and at 3 years at one site. The P/L ratio effects on viscosity and wetting were evaluated in vitro by determining the film thickness possible at different ratios. RESULTS: At 2 years the retention levels at the two sites differed significantly (p < or = 0.1). Site B ('low-wet' group) exhibited 100% retention, and Site A ('high-dry' group) exhibited 78% retention. At 3 years Site A exhibited 74% retention, and nine of the 12 retention failures occurred in patients 65 years and older. Laboratory measurements demonstrated that the viscosity of 'low-wet' mixtures permitted film thickness that were one-half those of the 'high-dry' group. CONCLUSIONS: The study demonstrated that a higher powder/liquid ratio and a drier dentine surface compromised wetting by a resin-modified glass-ionomer resulting in a decline in retention from baseline to 3 years. This study suggests that the dentine surface should be kept hydrated to promote bonding, and that the powder/liquid ratio should be low enough to create low-viscosity mixtures which promote wetting. In the 'high-dry' dentine group there was still 74% retention at 3 years, indicating that factors other than wetting affect retention.

The clinical performance of CAD-CAM-generated ceramic inlays: a four-year study.

The authors conducted a long-term clinical study of 50 CEREC (Siemens AG) CAD-CAM inlay restorations in 28 patients. After four years, they found the inlays to rate very highly in color matching, interfacial staining, secondary caries, anatomic contour, marginal adaptation, surface texture and postoperative sensitivity. They monitored cement loss along the occlusal margins and found it to be relatively low, with an unusual decrease in measured cement wear from the third to the fourth year. The favorable results of this long-term clinical study of these CAD-CAM restorations portend significant success for this restorative approach.

Contributing co-variables in clinical trials.

To accurately compare Class V dentinal bonding studies, it is essential to critically classify the effects of the intraoral location and age of the patient on the retention of resin composite restorations. A mathematical formula for normalization combined with the Weibull analysis also is proposed that could provide CL50 values for the clinical longevity of adhesive restorations.

Examining tooth flexure effects on cervical restorations: a two-year clinical study.

This study evaluated the clinical performance of dentinal adhesives in seven various material/technique combinations. No statistically significant differences were observed among the restorative combinations, or among technique variables after two years in terms of retention, sensitivity or USPHS categories. However, other factors related to tooth flexure--such as occlusal stress, patient age, restorative material and restoration location--showed statistically significant associations with retention failures. These results support a tooth flexural theory of restoration retention.

Correlation of M-L, Leinfelder, and USPHS clinical evaluation techniques for wear.

Most recent clinical research studies on wear of posterior composite restorations have used the USPHS and Leinfelder measuring techniques. New studies are adopting the Moffa-Lugassy (M-L) technique. However, to date there has been no means of comparing results of the different techniques. The objective of this study was to correlate the M-L scale wear values to Leinfelder scale wear values and to USPHS scale alfa-bravo transitions, so that data can be pooled across studies for comparisons. M-L evaluations were made for 221 restorations previously evaluated by the USPHS and Leinfelder methods. The M-L wear values were determined as the mean of three independent evaluators' values. At the USPHS alfa-bravo transition, the mean Leinfelder wear value was 192 microns, and the mean M-L value was 97 microns. The correlation coefficient for the linear regression of M-L values vs. Leinfelder values was 0.87. The scales were linearly related, with a slope of 0.52. The average values for M-L readings of wear were statistically different and approximately half the Leinfelder values.

Comparison of direct and indirect methods for analyzing wear of posterior composite restorations.

The vast majority of recent clinical research involving wear analyses of posterior composite resin restorations have used either the direct evaluation method (USPHS) or the indirect cast comparison (Leinfelder) method. However, there has never been any established correlation of the two wear scales. The objective of this study was to determine the amount of wear for the USPHS alfa-bravo transition on the basis of cast comparison data. Clinical wear data were collected over five years by both the direct method and the indirect method. Three materials were used involving a total of 221 restorations in 61 patients. Each restoration was evaluated at baseline, six months, one, two, three, and five years by each method. Then, for those restorations which underwent a transition from an alfa to a bravo clinical rating, the absolute wear at the transition was determined by averaging the indirect ratings just before and just after the transition. The mean wear corresponding to the alfa-bravo transition was 192 +/- 60 microns. Because of the large width of the alfa category up to the alfa-bravo transition, extensive early changes and high initial wear rates cannot be detected by the USPHS system.

Stress in patients with pain in the muscles of mastication and the temporomandibular joints.

This study examined the role of stress in subjects having combined muscle and temporomandibular joint pain compared to subjects having only muscle pain or only joint pain. It was found that the combined pain (n = 39) and muscle pain (n = 24) groups had comparable levels of pain intensity and activity impairment. The combined pain group, however, had the lowest level of stress and was rated lower than the muscle group in clinicians ratings of psychological factors, stress and chronicity. The combined pain group and joint pain group (n = 28) were found to be comparable in terms of the clinician's ratings. This data does not support the concept of a progression of symptoms from muscle pain to combined muscle and joint pain that would be expected from a stress-induced muscle hyperactivity model of temporomandibular disorders.

Twelve-month clinical study of dentinal adhesives in class V cervical lesions.

Recently, numerous resin systems claiming dentinal adhesive properties have been introduced. This study evaluated the clinical performance of two such adhesive resins in seven various material and technique combinations without conventional cavity-retention features. To identify potential risk factors in regard to retention, nonmaterial- and technique-related variables such as patient age and occlusion were also evaluated.

Stress as a factor in muscle and temporomandibular joint pain.

Stress-induced muscle hyperactivity has been proposed as a major aetiological factor in the production of pain in the muscles of mastication and the temporomandibular joints. In the present study, a total of fifty-two patients with joint or muscle pain were evaluated for stress with the Derogatis Stress Profile (DSP). The muscle pain group (n = 24) had higher clinician ratings of psychological factors, stress and chronicity. The muscle-pain group also had higher Environmental Stress scores on the DSP, more intense pain, and more activity impairment than the joint-pain group (n = 28). The results of multiple regression analysis suggest an association between pain, depression, and impairment of activity in the muscle-pain group but not in the joint-pain group. The overall results further suggest that muscle pain develops at 'normal' levels of stress.

Correlates of dental student stress.

The purpose of this study is to identify correlates of dental student stress. Associations between characteristics of dental students and their stress levels are examined, along with the association of stress with drug use and health problems. A total of 300 out of 315 dental students completed a questionnaire that measured the frequency and stressfulness of 31 stressors; drug use; health problems; and student characteristics including Type A behavior, career commitment, demographics, and lifestyle variables. Characteristics that were associated with a higher stress level were a higher level of Type A behavior and lower level of career commitment. Greater stress was also associated with a greater frequency of health problems. The results suggest an interactional stress model in which the personalities and attitudes of students are important mediators of the stress response.