Franz Sebastian Schwindling

Clinical assessment of enamel wear caused by monolithic zirconia crowns

The purpose of this study was to measure enamel wear caused by antagonistic monolithic zirconia crowns and to compare this with enamel wear caused by contralateral natural antagonists. Twenty monolithic zirconia full molar crowns were placed in 20 patients. Patients with high activity of the masseter muscle at night (bruxism) were excluded. For analysis of wear, vinylpolysiloxane impressions were prepared after crown incorporation and at 6-, 12-, and 24-month follow-up. Wear of the occlusal contact areas of the crowns, of their natural antagonists, and of two contralateral natural antagonists (control teeth) was measured by use of plaster replicas and a 3D laser-scanning device. Differences of wear between the zirconia crown antagonists and the control teeth were investigated by means of two-sided paired Students t-tests and linear regression analysis. After 2 years, mean vertical loss was 46 μm for enamel opposed to zirconia, 19-26 μm for contralateral control teeth and 14 μm for zirconia crowns. Maximum vertical loss was 151 μm for enamel opposed to zirconia, 75-115 μm for control teeth and 60 μm for zirconia crowns. Statistical analysis revealed significant differences between wear of enamel by zirconia-opposed teeth and by control teeth. Gender, which significantly affected wear, was identified as a possible confounder. Monolithic zirconia crowns generated more wear of opposed enamel than did natural teeth. Because of the greater wear caused by other dental ceramics, the use of monolithic zirconia crowns may be justified.

A comparison of two digital techniques for the fabrication of complete removable dental prostheses: A pilot clinical study

STATEMENT OF PROBLEM The introduction of digital techniques might improve the quality and cost-effectiveness of treatment with complete removable dental prostheses (CDs). PURPOSE The purpose of this pilot clinical trial was to study and compare the clinical feasibility, complications during fabrication, and quality of 2 types of digitally designed CDs. MATERIAL AND METHODS Five participants were recruited into this preliminary clinical trial. For each participant, 2 pairs of digital CDs were designed. Prosthesis bases were fabricated by using identical data, either by milling from polymethyl methacrylate blanks or by injection molding. The treatment involved 4 clinical appointments. Polyvinyl siloxane impressions were made with custom trays and were subsequently digitalized. After evaluating esthetics and function with trial dentures, the CD bases were fabricated. To evaluate the workflow and quality of the prostheses, the clinical outcome was measured on 6-point scales ranging from poor (grade 6) to excellent (grade 1). For both prosthesis types, the following aspects were examined: fit, retention, esthetics, phonetics, maxillomandibular relation, and occlusion. RESULTS Both types of digital CDs could be fabricated without major complications. Only a few minor complications occurred during the fabrication process, predominantly esthetic issues. No pronounced difference was found between the prostheses concerning functional aspects. The definitive esthetic outcome was rated as very good. CONCLUSIONS The CDs fabricated using digital technology met the clinical requirements. However, more research is needed to confirm the results of this investigation.

Fracture resistance of glazed, full-contour ZLS incisor crowns

PURPOSE To compare the failure behaviour of zirconia-reinforced lithium silicate (Celtra Duo, DeguDent) with that of lithium disilicate (IPS e.max CAD, Ivoclar Vivadent) and feldspar (Mark II, VITA) ceramics. METHODS Three groups of sixteen glazed maxillary incisor crowns were produced. The inner surfaces of the crowns were etched, then luted to metal dies with self-adhesive cement. Single load-to-failure tests were performed before and after thermo-mechanical ageing. To simulate clinical conditions, the specimens were thermocycled (10,000 cycles between 6.5°C and 60°C) and underwent chewing simulation (1,200,000 cycles, Fmax=86N). Statistical analyses were performed by use of non-parametric Kruskal-Wallis and Mann-Whitney U-tests. RESULTS Before ageing, all the monolithic incisor crowns fractured at test forces >285N. Mean fracture loads were highest for zirconia-reinforced lithium silicate (725N, SD 162N), slightly lower for lithium disilicate (701N, SD 276N), and lowest for feldspar (554N, SD 190N). The differences between the results were not statistically significant. After ageing, fracture resistance decreased for all materials except zirconia-reinforced lithium silicate. Mean fracture loads were highest for zirconia-reinforced lithium silicate (766N, SD 98N) and significantly lower for both lithium disilicate (485N, SD 64N) and feldspar (372N, SD 116N). CONCLUSION Monolithic restorations fabricated from zirconia-reinforced lithium silicate retain high fracture resistance after extensive thermo-mechanical ageing. This preclinical study suggests that cohesive failures of monolithic anterior crowns produced of these ceramics will not be a major problem in dental practice.

Mini dental implants retaining mandibular overdentures: A dental practice-based retrospective analysis

PURPOSE The purpose of this study was to assess the survival of mini dental implants (MDI) and to measure prosthetic maintenance needs in a dental practice-based setting. METHODS Patients with mandibular removable dentures were provided with MDI to improve denture retention. Complications and maintenance were analyzed by use of patient records and evaluated with Kaplan-Meier curves and the log rank test at a significance level of 0.05. RESULTS Ninety-nine MDI were placed in 25 patients (mean age: 72 years). Two MDI fractured during placement and eight implants failed during the first weeks. No more implants were lost for up to seven years, resulting in 92% survival. Implant survival differed significantly depending on whether the maxilla was provided with complete dentures (94.9%) or with partial dentures (81%). All prostheses were in use at the time of data extraction. Denture base fractures were observed in six cases, an incidence of fractures of 24%. Some minor intervention was necessary: one resin tooth fractured, retention rings were changed in five cases, and repeated relining was required for 16% of the dentures. CONCLUSIONS After mid-term observation, survival of MDI was good. However, the incidence of denture base fractures and of minor prosthetic complications should not be under-estimated.

Retention behavior of double-crown attachments with zirconia primary and secondary crowns

OBJECTIVE To investigate whether adequate retention of zirconia conical crown (CC) attachments can be achieved, and to investigate their long-term retention. METHODS Sixteen individual zirconia primary crowns were produced with convergence angles of 1° or 2° (eight of each). After determination of the convergence angles of the primary crowns, monolithic zirconia secondary crowns were manufactured. To evaluate the retention behavior of all-zirconia CC, the crowns were fitted with forces from F=12.5-100 N. Force magnitudes during the loosening process (L) were then measured. L/F ratios were recorded and the coefficient of friction (μ0) was calculated. Long-term retention was tested with up to 50,000 cycles of denture integration at a speed of 30 mms(-1) and a fitting force magnitude of 53 N. RESULTS Even when primary crowns were manufactured with the utmost care, the real convergence angles were greater than the nominal angles of the standardized burs (1° and 2°) by 0.28° (SD 0.11°). Without mechanical aging, mean L/F was 0.632 (SD 0.038) for 1° samples and 0.526 (SD 0.022) for 2° samples, indicative of high retentive forces of up to 63.2% of the fitting forces. When all the test results were used, best-fitting curves gave μ0=0.117 for new samples and μ0=0.126 for samples after 50,000 integration cycles. SIGNIFICANCE When the correct milling and sintering parameters are chosen, the retention behavior of zirconia CCs is adequate and stable. This innovative type of attachment is appealing because of the beneficial properties of zirconia and the efficient CAD/CAM-based manufacture.

In vitro investigation on extensively destroyed vital teeth: is fracture force a limiting factor for direct restoration?

To evaluate the in vitro fracture load of extensively damaged vital teeth after either direct or indirect restauration, severe tooth substance loss was simulated for 96 molars. Subsequently, two cavities were prepared with little (design 1) or more substantial (design 2) residual tooth support. All molars were provided with a 2-mm ferrule design and then divided into 12 test groups based on their occlusal surface size. They were restored with composite or with either of two types of single crown (cast metal or milled zirconia). After thermal ageing (10,000 cycles at 6.5 and 60 °C), 1.2 million cycles of chewing simulation were applied (64 N). Maximum fracture load was determined with a loading angle of 45°. Statistical analysis was performed by use of Kaplan-Meier modelling, Students t-tests, one-way anova, post hoc Tukeys HSD tests and linear regression analysis. Regarding mean fracture load without ageing, the indirect restorations outperformed composite (design 1: direct: 508 ± 123 N, indirect: 741 ± 248 N; design 2: direct: 554 ± 167 N, indirect: 903 ± 221 N). After artificial ageing, however, these differences were no longer significant (design 1: direct: 328 ± 189 N, indirect: 506 ± 352 N; design 2: direct 399 ± 208 N, indirect 577 ± 292 N). Instead, the fracture load of the aged composite restorations was comparable with that for zirconia (design 1) and cast metal (design 2) crowns. Fracture loads of direct composite restorations after artificial ageing might fulfil clinical requirements.

Determination of the palatal masticatory mucosa thickness by dental MRI: a prospective study analysing age and gender effects

OBJECTIVES The aim of this prospective study was to evaluate age and gender effects on the palatal masticatory mucosa thickness by using non-invasive and non-ionizing MRI. METHODS 40 periodontally healthy participants of five gender-balanced age groups (20-29, 30-39, 40-49, 50-59 and 60-69 years, respectively) underwent dental MRI at 3 Tesla using a contrast-enhanced, high-resolution 3D-sequence. The palatal masticatory mucosa was measured at 40 standard measurement points by two independent observers. Statistical analysis was performed by using intraclass correlation coefficient (ICC), Shapiro-Wilk test, two-way analysis of variance and post-hoc Tukey HSD test. RESULTS Measurements of the palatal masticatory mucosa thickness were highly reliable with a mean intraobserver ICC of 0.989 and a mean interobserver ICC of 0.987. Mean palatal masticatory mucosa thickness increased with the distance from the gingival margin in all tooth regions. Molars showed a considerably lower average palatal masticatory mucosa thickness at intermediate heights in comparison to canines and premolars. Average palatal masticatory mucosa thickness continuously increased with age and significantly differed between age groups (p < 0.01). A significant increase was observed between the age groups of 30-39 years and 40-49 years (p = 0.04). Gender had no significant effect on average palatal mucosa thickness (p = 0.19). However, there was a tendency towards thicker mucosa in males (mean ± SD, 3.36 mm ± 0.47) compared to females (3.23 mm ± 0.44). CONCLUSIONS In the present study, dental MRI allowed for a highly reliable determination of the palatal masticatory mucosa thickness. Considerable intra- and interindividual variations in palatal masticatory mucosa thickness were observed. Average palatal masticatory mucosa thickness was dependent on age but not on gender.

The single mandibular implant study – Short-term effects of the loading protocol on Oral Health-related Quality of Life

PURPOSE A single implant can be placed to retain an overdenture in the edentulous mandible. This study aimed at the development of Oral Health-related Quality of Life comparing immediate and delayed implant loading, i.e., loading after 3 months of submerged healing. METHODS In a randomized controlled trial, 158 participants received a single mandibular implant in the midline. Quality of life was measured using the summary score of the German 49-item Oral Health Impact Profile at baseline, one month after implant placement (direct loading group) as well as one and four months after loading. RESULTS Mean scores at baseline were comparable. Four months after implantation, a decrease of mean scores was recognized for both groups, indicating a significantly enhanced quality of life after treatment. When comparing the groups after both 1 and 4 months of loading, quality of life was insignificantly higher in the delayed loading group (1 month: 42.1 vs. 32.3; 4 months: 33.6 vs. 27.7). For immediate loading, an insignificant tendency to an earlier improvement was recognized (Δ1month-baseline: 9.7, compared to Δ1month-baseline: 6.4). CONCLUSIONS The single mandibular implant concept was associated with a positive impact on quality of life. However, no statistically significant influence of implant loading on quality of life was found.

Long-term success of oral health intervention among care-dependent institutionalized seniors: Findings from a controlled clinical trial

OBJECTIVES The purpose of this work was to investigate the long-term effectiveness of oral health education of caregivers in nursing homes with care-dependent and cognitively impaired residents. METHODS Fourteen nursing homes with a total of 269 residents were allocated to a control group, with continued normal care, or to an intervention group. Allocation was performed at nursing home level. In the intervention group, caregivers were given oral health education, and ultrasonic cleaning devices were provided to clean removable prostheses. Oral health was assessed at baseline and after 6 and 12 months by use of the Plaque Control Record (PCR), Gingival Bleeding Index (GBI), Community Periodontal Index of Treatment Needs (CPITN) and Denture Hygiene Index (DHI). Mixed models for repeated measures were performed for each target variable, with possible confounding factors (intervention/control group, age, sex, residence location and care-dependence). RESULTS In the control group, no changes of target variables were observed between baseline and the 6- and 12-month follow-ups. After 6 and 12 months, PCR and DHI were significantly improved in the intervention group. For PCR, the intergroup difference of improvements was -14.4 (95% CI: -21.8; -6.9) after 6 months. After 12 months, the difference was -16.2 (95% CI: -27.7; -4.7). For DHI, the intergroup difference compared to baseline was -15 (95% CI: -23.6; -6.5) after 6 months and -13.3 (95% CI: -24.9; -1.8) after 12 months. There was neither a statistically significant effect on GBI nor on CPITN. Care-dependency showed a substantial trend to smaller improvements in PCR (P = .074), while an inverse effect was apparent for DHI (P < .001). CONCLUSIONS Education of caregivers improves and maintains the oral health of care-dependent nursing home residents over longer periods. Use of ultrasonic devices is a promising means of improving denture hygiene among the severely care-dependent. Such interventions can be easily and cheaply implemented in routine daily care.

MSVAT-SPACE-STIR and SEMAC-STIR for Reduction of Metallic Artifacts in 3T Head and Neck MRI

BACKGROUND AND PURPOSE: The incidence of metallic dental restorations and implants is increasing, and head and neck MR imaging is becoming challenging regarding artifacts. Our aim was to evaluate whether multiple-slab acquisition with view angle tilting gradient based on a sampling perfection with application-optimized contrasts by using different flip angle evolution (MSVAT-SPACE)-STIR and slice-encoding for metal artifact correction (SEMAC)-STIR are beneficial regarding artifact suppression compared with the SPACE-STIR and TSE-STIR in vitro and in vivo. MATERIALS AND METHODS: At 3T, 3D artifacts of 2 dental implants, supporting different single crowns, were evaluated. Image quality was evaluated quantitatively (normalized signal-to-noise ratio) and qualitatively (2 reads by 2 blinded radiologists). Feasibility was tested in vivo in 5 volunteers and 5 patients, respectively. RESULTS: Maximum achievable resolution and the normalized signal-to-noise ratio of MSVAT-SPACE-STIR were higher compared with SEMAC-STIR. Performance in terms of artifact correction was dependent on the material composition. For highly paramagnetic materials, SEMAC-STIR was superior to MSVAT-SPACE-STIR (27.8% smaller artifact volume) and TSE-STIR (93.2% less slice distortion). However, MSVAT-SPACE-STIR reduced the artifact size compared with SPACE-STIR by 71.5%. For low-paramagnetic materials, MSVAT-SPACE-STIR performed as well as SEMAC-STIR. Furthermore, MSVAT-SPACE-STIR decreased artifact volume by 69.5% compared with SPACE-STIR. The image quality of all sequences did not differ systematically. In vivo results were comparable with in vitro results. CONCLUSIONS: Regarding susceptibility artifacts and acquisition time, MSVAT-SPACE-STIR might be advantageous over SPACE-STIR for high-resolution and isotropic head and neck imaging. Only for materials with high-susceptibility differences to soft tissue, the use of SEMAC-STIR might be beneficial. Within limited acquisition times, SEMAC-STIR cannot exploit its full advantage over TSE-STIR regarding artifact suppression.