Faculty Publications (HBMCDM)

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Whole Salivary Interleukin-6 and Matrix Metalloproteinase-8 Levels in Patients With Chronic Periodontitis With and Without Prediabetes
(2013-09) Bain, Crawford
Background: The cytokine profile in unstimulated whole saliva (UWS) of patients with prediabetes and chronic periodontitis (CP) remains uninvestigated. The aim of this study is to assess interleukin (IL)-6 and matrix metalloproteinase (MMP)-8 levels in UWS of patients with CP with and without prediabetes. Methods: Eighty-eight males (aged 39 to 51 years) were divided into three groups: group 1: 28 patients with CP and prediabetes; group 2: 30 patients with CP and without prediabetes; and group 3: 30 controls. Fasting blood glucose (FBG) and hemoglobin A1c (HbA1c) levels, periodontal parameters (plaque index, bleeding on probing, probing depth, attachment loss, and marginal bone loss), and number of missing teeth were recorded. UWS samples were collected, and UWS flow rate (UWSFR) was measured. IL-6 and MMP-8 were measured in UWS using enzyme-linked immunosorbent assay. P values <0.05 were considered statistically significant. Results: Mean FBG and HbA1c levels were significantly higher in group 1 (119.3 –3.1 mg/dL and 6.1% –0.2%) than group 2 (80.1 –3.5 mg/dL and 4.8% –0.5%; P <0.001) and group 3 (75.3 –2.2 mg/dL and 4.3% –0.2%; P <0.05). UWSFR was significantly higher in groups 2 (0.53 –0.1 mL/ minute; P <0.05) and 3 (0.51 –0.1 mL/minute; P <0.01) than group 1 (0.33 –0.05 mL/minute). Periodontal parameters were worse in group 1 (P <0.05) and group 2 (P <0.05) than group 3. There was no difference in periodontal parameters, numbers of missing teeth, or salivary IL-6 and MMP-8 levels between patients in groups 1 and 2. Conclusion: Salivary IL-6 and MMP-8 levels are elevated in patients with CP with and without prediabetes.
Current Guidelines for the Use of Fluoride in Pediatric Dentistry, A Review
(2014) El-Halabi, Manal
Abstract: Fluoride use as a chemotherapeutic agent for caries prevention has been well researched and documented. The recommendations for the use of fluoride have evolved through the years as a result of many factors. The change in the prevalence of caries and the advent of different fluoride formulations along with the desire to maximize the benefits and minimize the side effects lead many authorities to set guidelines for the use of different formulations of fluoride. This review attempts to summarize the most current evidence-based guidelines of fluoride therapy put forth by various organizations worldwide. The review includes guidelines on community water fluoridation, fluoride supplements, fluoride toothpaste, professionally applied fluorides and fluoride mouth rinses.
Severity of early childhood caries in preschool children attending Al-Ain Dental Centre, United Arab Emirates
(2014) Kowash, Mawlood B.
Aim: To investigate the severity of and contributing factors of early childhood caries (ECC) in preschool children presented to a paediatric dentistry department in Al-Ain Dental Centre, United Arab Emirates; to study the level of any previous dental care provided to these children and to establish a baseline database for further research and the resources required for serving preschool children in Al-Ain (UAE). Study design: Cross-sectional prospective. Methods: The sample consisted of all healthy children below 5 years of age who presented for their initial visits to the Department of Paediatric Dentistry during a 3-month period. A structured questionnaire was used to obtain information regarding demographic data, feeding history and dietary habits, and oral hygiene practices. The dental examination of children was conducted by the investigator with the help of a mouth mirror and Sirona dental unit light source. Results: One hundred and seventy six children with a mean age of 3.7 years were included in the study and 78 (44 %) children were still bottle-fed on demand at the time of examination. More than half of the children consumed sweets more than once/day and 58 % either never or rarely brushed their teeth. Only one child was given fluoride. Two-thirds of children had never visited a dentist before and 63 % had poor oral hygiene. The mean dmft and dmfs scores were 10.9 and 32.1, respectively. The care index was very low (6.4 %). Conclusion: The high level of dental decay could be attributed to on-demand bottle feeding, high sweet consumption, poor oral hygiene, lack of use of fluoride prevention and lack of regular dental visits. There is a great need for prospective studies and community preventive programmes to solve the continuing problem of ECC.
Reporting characteristics of meta-analyses in orthodontics: methodological assessment and statistical recommendations
(2014) Athanasiou, Athanasios E.
Abstract: Ideally meta-analyses (MAs) should consolidate the characteristics of orthodontic research in order to produce an evidence-based answer. However severe flaws are frequently observed in most of them. The aim of this study was to evaluate the statistical methods, the methodology, and the quality characteristics of orthodontic MAs and to assess their reporting quality during the last years. Electronic databases were searched for MAs (with or without a proper systematic review) in the field of orthodontics, indexed up to 2011. The AMSTAR tool was used for quality assessment of the included articles. Data were analyzed with Student’s t-test, one-way ANOVA, and generalized linear modelling. Risk ratios with 95% confidence intervals were calculated to represent changes during the years in reporting of key items associated with quality. A total of 80 MAs with 1086 primary studies were included in this evaluation. Using the AMSTAR tool, 25 (27.3%) of the MAs were found to be of low quality, 37 (46.3%) of medium quality, and 18 (22.5%) of high quality. Specific characteristics like explicit protocol definition, extensive searches, and quality assessment of included trials were associated with a higher AMSTAR score. Model selection and dealing with heterogeneity or publication bias were often problematic in the identified reviews. The number of published orthodontic MAs is constantly increasing, while their overall quality is considered to range from low to medium. Although the number of MAs of medium and high level seems lately to rise, several other aspects need improvement to increase their overall quality.
Effect of nonsurgical periodontal therapy (with or without oral doxycycline delivery) on glycemic status and clinical periodontal parameters in patients with prediabetes: a short-term longitudinal randomized case-control study
(2014-01-22) Bain, Crawford
Objective: The aim of the present short-term longitudinal randomized case–control study was to assess the effect of nonsurgical periodontal therapy (NSPT) (with and without oral doxycycline delivery) on glycemic status and clinical periodontal parameters in patients with prediabetes. Material and methods: Sixty-six patients with prediabetes and periodontal disease were included. Characteristics of the study cohort (age, gender, socioeconomic status [SES] education status, duration of prediabetes, and type of treatment adopted for prediabetes management) were recorded. Patients were randomly divided into two groups (33 patients/group). In group 1, scaling and root planing (SRP) was performed, and in group-2, patients underwent SRP and oral doxycycline (100 mg) administration once daily for 15 days. In each group, the following parameters were investigated at baseline and after 3 months: (a) fasting blood glucose level (FBGL), (b) hemoglobin A1c (HbA1c), and (c) periodontal parameters (plaque index [PI], bleeding on probing [BOP], probing depth [PD], and clinical attachment loss [AL]). Statistical analysis was performed using Student’s test. Results: There was no significant difference in age, gender, SES, education status, and duration and treatment of prediabetes among individuals in groups 1 and 2. Three months post-NSPT, FBGL and HbA1c were significantly reduced among patients in group 1 (P < 0.05) and group 2 (P < 0.05) compared to baseline. Three months post-NSPT, PI (P < 0.05), BOP (P < 0.05), and PD (P < 0.05) were significantly reduced among patients in group 1 (P < 0.05) and group 2 (P < 0.05) compared to baseline. There was no difference in clinical AL between the groups after 3 months of NSPT. Conclusion: NSPT (with and without oral doxycycline delivery) reduces hyperglycemia and periodontal inflammation in patients with prediabetes.
Amelogenesis imperfecta and anterior open bite: Etiological, classification, clinical and management interrelationships
(2014-03) Athanasiou, Athanasios E
Abstract: Although amelogenesis imperfecta is not a common dental pathological condition, its etiological, classification, clinical and management aspects have been addressed extensively in the scientific literature. Of special clinical consideration is the frequent co-existence of amelogenesis imperfecta with the anterior open bite. This paper provides an updated review on amelogenesis imperfecta as well as anterior open bite, in general, and documents the association of these two separate entities, in particular. Diagnosis and treatment of amelogenesis imperfecta patients presenting also with anterior open bite require a lengthy, comprehensive and multidisciplinary approach, which should aim to successfully address all dental, occlusal, developmental, skeletal and soft tissue problems associated with these two serious clinical conditions.
Effect of intraoral aging on the setting status of resin composite and glass ionomer orthodontic adhesives
(2014-04) Athanasiou, Athanasios E.
Introduction: The aim of this study was to assess the effect of intraoral aging on the setting status of a resin composite and a glass ionomer adhesive, relative to control specimens stored in water. Methods: Metallic brackets were bonded with resin composite orthodontic adhesive (Transbond XT; 3M Unitek, Monrovia, Calif) or a glass ionomer cement (Fuji I; GC, Tokyo, Japan) to recently extracted premolars and kept in water for 6 months. The same materials were also bonded to the premolars of orthodontic patients. After 6 months, the teeth were carefully extracted, with the brackets intact on their buccal surfaces. All teeth were embedded in epoxy resin and sectioned buccolingually. Fourier transform infrared microscopy and Raman microscopy were used for the estimation of the degree of cure in the composite and the salt yield in the glass ionomer adhesives. Results: The control samples of the composite showed significantly lower degrees of cure than did the retrieved specimens (52.40% ± 3.21% vs 57.62% ± 1.32% by Fourier transform infrared microscopy, and 61.40% ± 2.61% vs 67.40% ± 3.44% by Raman microscopy). Raman microscopy significantly overestimated the degree of cure and failed to provide reliable information for the salt yield in the glass ionomer cement. Fourier transform infrared microscopy showed increased, but no statistically significant difference in, aluminum-carboxylate salts in the retrieved specimens.
Assessing small study effects and publication bias in orthodontic meta-analyses: a meta-epidemiological study
(2014-05) Athanasiou, Athanasios E
Objective: The aim of this study was to examine the presence and extent of small study effects and publication bias in meta-analyses (MAs) based on orthodontic studies. Materials and methods: Following an extensive literature search, 25 MAs including 313 studies were identified and were possible to be re-analyzed. For the assessment of publication bias, contour-enhanced funnel plots were examined and their symmetry was tested using the Begg and Mazumdar rank correlation and Egger's linear regression tests. Robustness of MAs' results to publication bias was examined by Rosenthal's failsafe N, and adjusted effect sizes were calculated after consideration of publication bias using Duval and Tweedie's "trim and fill" procedure. Results: Only few of the originally published MAs assessed the existence and effect of publication bias and some only partially. Inspection of the funnel plots indicated possible asymmetry, which was confirmed by Begg and Mazumdar's test in 12 % and by Egger's test in 28 % of the MAs. According to Rosenthal's criterion, 62 % of the MAs were robust, while adjusted effect estimates with unpublished studies differed from little to great from the unadjusted ones. Pooling of Egger's intercepts of included MAs indicated that evidence of asymmetry was found in the orthodontic literature, which was accentuated in medical journals and in diagnostic MAs. Conclusions: Small study effects and publication bias can often distort results of MAs. Since indications of publication bias in orthodontics were found, the influence of small trials on estimated treatment effects should be routinely and more carefully assessed by authors conducting MAs.
Oral and Dental Considerations in the Management of Leukemic Children
(2014-09) Alnuaimi, Eman H; El-Halabi, Manal; Kowash, Mawlood B.
Abstract: An incidence of overall oral sequelae in leukemic children of 54% has been reported in the literature. Oral complications include mucositis, fungal and viral infections, salivary gland hypofunction, dental caries, and others. Mucositis accounts for the most common complication followed by fungal infections and viral infections. It has also been reported that the quality of life of these children is affected. Dental healthcare professionals play a very important role in assessing the patient’s oral health needs before, during, and after cancer therapy. A multidisciplinary approach between the medical and dental team will help prevent, stabilize, and treat the oral and dental problems at an early stage. This paper reviews briefly the oral health problems in leukemic children as well as dental considerations and recommendations for optimal oral health care.
Effect of Mandibular Repositioning Appliances on Inspiratory and Expiratory Total Air
(2014-09) Mageet AO
Abstract: Obstructive Sleep Apnoea / Hypopnoea Syndrome (OSAHS) is associated with obstruction of the upper airway and occurs as a result of repeated closure of the upper airway during sleep, either by anatomical or patho-physiological factors. During these episodes, the diaphragm and chest muscles involved in breathing work actively to re-open the occluded airway and suck air into the lungs. The aim of this study is to clinically investigate the changes in inspiratory and expiratory total air when a mandibular repositioning appliance (MRA) was used for the treatment of OSAHS and to suggest possible improvement in research technology when using the MRA. A twenty three OSAHS white Caucasian male patients were randomly selected and evaluated against twenty three non-apnoeic subjects matched for race and sex from Fife region, Scotland. Anthropometric comparison is done for the body mass index (BMI) and the percentage of predicted neck circumference (PPNC). Rhinomanometer tests were used for the OSAHS patients and control before wearing the appliance and for the OSAHS group before and after wearing the MRA. Significant improvements of inspiratory and expiratory total air have resulted. MRA is useful alternative or adjunct to the use of Continuous Positive Airway Pressure (CPAP) devices in selected patients with snoring and mild to moderate (OSAHS).
Severity of Depression among Elderly Women Attending Holy Quran Memorization Centers in Saudi Arabia
(2014-09-28) Hassan Khamis, Amar
Background: Depression is the most common mental health problem among the elderly, causing considerable morbidity worldwide, as well as increased healthcare costs. The purpose of this study was to determine the severity of depression among Saudi elderly women attending Quran Memorization Centers in the Kingdom of Saudi Arabia. Methods: We recruited 340 participants aged 65 years and older from 11 Quran Memorization Centers in the cities of Dammam, Khobar and Dhahran in the Eastern Province of Saudi Arabia. We used a structured interview questionnaire composed of socio-demographic characteristics and the Activity of Daily Living instrument to assess participants’ physical, social, and health-status conditions. In addition, we used the English version of the Geriatric Depression Scale and the Arabic version of Montreal Cognitive Assessment as the main screening instruments for depression and cognitive impairment respectively. Results: Severity of depression among all participants was 42.1%. Low monthly income, the absence of a caregiver, diabetes, disability, and sleep disturbance were identified as common factors associated with depression. Conclusion: The present study showed that depression in elderly females attending these centers was high and associated with multiple medical and socioeconomic characteristics, which is a cause of concern.
In vitro spectrophotometric evaluation of Vivera® clear thermoplastic retainer discolouration
(2014-11) Athanasiou, Athanasios E.
Aims: To investigate the in vitro effect of different staining solutions on the colour stability of Vivera® retainers. Methods: Thirty flat specimens fabricated using the Vivera® material (Align Technology Inc., CA, USA) were assigned into five Groups (A, B, C, D and E) and immersed at 37°C in solutions of distilled water (control), coffee, tea, red wine, and Coca-Cola®. The CIE colour parameters (L*, a*, b*) of each specimen were measured before immersion (T0) and after 12 hours (T1), three days (T2) and seven days (T3) of solution exposure. Colour differences (ΔΕ) between the interval groups were calculated. Results: Significant differences were observed concerning (i) L* between T3 and T0, T1 and T2 for Group B; (ii) a* between T0 and T1, T2 and T3 for Groups B, C, D and E, as well as between T1 and T2 for Group C; and (iii) b* between T0 and T1, T2 and T3 for Group B and between T0 and T2 and T3 for Group C. The differences between ΔΕ(T1-T0), ΔΕ(T2-T0) and ΔΕ(T3-T0) were statistically significant for Groups B and C, as well as the difference between ΔΕ(T1-T0) and ΔΕ(T2-T0) for Group D. Conclusions: Coffee, tea and red wine caused visible changes in the retainers’ colour.
Evaluation of Calcified Carotid Artery Atheromas Detected By Panoramic Radiograph among Patients with Type II Diabetes Mellitus
(2015) Jaber, Mohamed A; Shah, Maanas S.; Abuzayda, Moosa
Abstract: This study was designed to determine the prevalence of Carotid artery calcifications (CACs) of diabetic patients and compare it with normal non-diabetic individuals. Panoramic radiographs of 200 adult patients with type 2 diabetes (90 male and 110 females) (age range 16-79 years; mean age 40.54 years) and 200 controls (age-match, free of systemic diseases) were examined on panoramic radiographs for any unusual radiopacity adjacent to or just below the intervertebral space between C3 and C4. Statistical analysis was carried out using chi-squared and Fisher exact tests. Carotid artery calcifications (CACs) were higher in diabetic patients compared with normal healthy control and the statistical difference between the two groups was significant (Chi-square test = 10.82, P = 0.001). Twenty-five (16 females, 9 males) diabetic patients showed CACs, Mean age of diabetic patients with calcification was 47.11 years. Further analysis of this group showed that 60% of patients with CACs were smokers, 48% had hypertension and 25% were obese. In conclusion, our study shows that in patients with diabetes mellitus CACs can be detected by panoramic radiography and the patients may benefit from a referral to physicians for further evaluation and necessary management.
The Minimal Important Difference (MID) as a criterion in evaluating the clinical significance of changes in the quality of life of orthognathic patients
(2015) Kaklamanos, Eleftherios G
Abstract: The Minimal Important Difference (MID) represents the smallest change patients perceive in their health status. It is a convenient criterion for evaluating the clinical significance of changes in Health-Related Quality of Life (HRQoL). This literature review aims at presenting a critical overview of the MID concept, the methods used to evaluate whether a change in HRQoL is lower or higher than the MID, and, finally, to research* the range of changes suggesting clinically significant differences in the HRQoL of orthognathic patients in the relevant literature. According to the modern scientific literature, the MID may help evaluate the clinical significance of changes measured in different trials from the patient’s perspective. Particularly in the case of patients undergoing orthognathic surgery, it could contribute to an in-depth analysis of the resulting benefits, understanding the process more holistically, and taking the most appropriate treatment decisions. To determine MID, the use of a combination of statistics-based methods, such as the Standard Error of Measurement (SEM), and methods based on anchors is recommended. Specifically, with respect to the HRQoL SF-36v1 (Short-Form-36 Health Survey version 1), the SIP (Sickness Impact Profile), the WHOQL-BREF (World Health Organization Quality of Life-BREF), the OHIP-14 (Oral Health Impact Profile-14) and the OQoLQ (Orthognathic Quality of Life Questionnaire), which have been used in the prospective evaluation of HRQoL in orthognathic patients, no relevant available MID values were found. A further systematic study of the MID concept in the quality of life of patients undergoing orthognathic surgery could help achieve a more comprehensive record of the impact of this treatment procedure on the patients’ physical and psychosocial well being.
Serum levels of folate and vitamin B12 in oral epithelial dysplasia
(2015) Jaber, Mohamed A
Abstract: Oral epithelial dysplasia (OED) is a histopathologic diagnosis associated with an increased risk of cancer. Deficiency of vitamin B12 and folate is associated with causation of certain precancerous and cancerous lesions. The aims of this study were: to evaluate the circulating levels of vitamin B12, folate status and iron, in patients with OED and to compare these levels with the values obtained in normal control subjects with and without tobacco smoking and alcohol drinking. To evaluate the circulating level of vitamin B12, serum folate, red blood cells folate and iron among OED patients. Data were collected from 120 patients with OED and 120 healthy control Subjects matched for age and gender, selected from patients with oral diseases not caused by tobacco or alcohol or related to knowing haematinic deficiency. Measurement of serum folate and vitamin B12 were carried out using radioassay. The majority of OED were graded either mild (46.7%) or moderate (40.0%) lesions and most of patients with OED were current smokers of more than 20 cigarettes per day for more than 20 years compared with normal healthy control. A significant decrease in the serum levels of folate, red blood cell folate was found in OED compared to normal tobacco smokers (p<0.05). No significant differences in vitamin B12 was found between OED cases and normal control subjects. Likewise significant differences in serum ferritin level were found between OED cases and normal drinkers of alcoholic beverages (p<0.05). And no significant differences in the TIBC level in OED compared with control subjects. These findings support the notion that OED may develop in persons who expose to tobacco smoking and have low folate level. A possible inverse association between iron concentrations and the risk of OED needs further study.
Trends in income-related inequality in untreated caries among children in the United States: findings from NHANES I, NHANES III, and NHANES 1999–2004
(2015) Chattopadhyay, Amit
Objective: The goal of this analysis was to describe income-related inequality in untreated caries among children in the United States over time. Methods: The analysis focuses on children ages 2–12 years in three nationally representative U.S. surveys: the National Health and Nutrition Examination Survey (NHANES) 1971–1974, NHANES 1988–1994, and NHANES 1999–2004. The outcome of interest is untreated dental caries. Various methods are employed to measure absolute and relative inequality within each survey such as pair-wise comparisons, measures of association (odds ratios), and three summary measures of overall inequality: the slope index of inequality, the relative index of inequality, and the concentration index. Inequality trends are then assessed by comparing these estimates across the three surveys. Results: Inequality was present in each of the three surveys analyzed. Whether measured on an absolute or relative scale, untreated caries disproportionately affected those with lower income. Trend analysis shows that, despite population-wide reductions in untreated caries between NHANES I and NHANES III, overall absolute inequality slightly increased, while overall relative inequality significantly increased. Between NHANES III and NHANES 1999–2004, both absolute and relative inequality tended to decrease; however, these changes were not statistically significant. Conclusions: Socioeconomic inequality in oral health is an important measure of progress in overall population health and a key input to inform health policies. This analysis shows the presence of socioeconomic inequality in oral health in the American child population, as well as changes in its magnitude over time. Further research is needed to determine the factors related to these changes and their relative contribution to inequality trends.
Comparison of Parental Satisfaction with Three Tooth-Colored Full- Coronal Restorations in Primary Maxillary Incisors
(2015) Salami, Anas
Objectives: To evaluate and compare the parental satisfaction among resin composite strip crown, pre-veneered stainless steel crown (PVSSC) and the newly introduced pre-fabricated primary zirconia crown for restoring maxillary primary incisors. Study design: A prospective clinical study on 39 children with carious or traumatized primary maxillary incisors. They were randomly and equally distributed in three groups and received one of the full-coronal restorations. Children were recalled to evaluate and compare parental satisfaction about performance of crowns after one year through a questionnaire. Results: Parents were satisfied with all three tooth colored full-coronal restoration techniques. A significant relationship was found between colour of PVSSC (p=0.003) and durability of resin strip crowns (p=0.009) with the overall parental satisfaction levels. Parents who gave poor ratings in these two variables however rated their overall acceptance levels as being satisfied. Conclusion: Parental overall satisfaction was highest for zirconia primary crowns followed by resin composite strip crowns and lowest satisfaction was reported for pre-veneered SSCs. Parents were least satisfied with durability of resin composite strip crowns and colour of pre-veneered stainless steel crowns. However, this did not affect their overall satisfaction with these crowns.
Use of Adhesive Techniques in the Management of Hypodontia
(2015) Al-Salehi, Samira
Abstract: The treatment and management of hypodontia are complex. Traditional treatments include the provision of conventional bridgework. Such treatment modalities are destructive of remaining tooth tissue particularly as the majority of patients presenting for treatment are young adults. This case report describes a 22 year old female Caucasian patient who was treated for missing permanent teeth using conservative adhesive non destructive techniques resulting in a pleasing aesthetic outcome.
IL-13 Polymorphism (IL-13 rs1800925 (-1055) (C/T) is Associated with Severe Hepatic Fibrosis in Human Schistosomiasis
(2015-01-25) Hassan Khamis, Amar
Abstract: An association study of a cohort of 177 Sudanese patients infected with Schistosoma mansoni {82 (46%) males and 95 (54%) females} was conducted to investigate the correlation of four polymorphisms {IFN-γ rs2069705 (C/T), IFN-γ R1 rs11914 (G/T), rs1327474 (A/G), and IL-13 rs1800925 (-1055) (C/T)} to the regression and progression of liver fibrosis 39 months after treatment with praziquantel (PZQ). Regression and progression phenotypes were evaluated by ultrasound. DNA from patients infected with S. mansoni was extracted, purified and amplified by PCR. Allelic typing was done using RFLP, primer extension reaction, DHPLC, and allelic discrimination assays (TAQ-MAN). SDS (Sequence Detection Systems) software was used for genotyping. There was an association between IL-13 rs1800925 T allele and the low grades of periportal fibrosis (PPF) (P = 0.02). No significant association was found between three polymorphisms (IFN-γ rs2069705 (C/T) P = 0.5, rs1327474 (A/G) P = 0.3 and IFN-γ R1 rs11914 (G/T), and PPF as response to PZQ. We conclude that IL-13 rs1800925 T allele is protective against PPF (P = 0.02).
Fracture resistance of porcelain veneered zirconia crowns with exposed lingual zirconia for anterior teeth after thermal cycling: An in vitro study
(2015-01-30) Amir-Rad, Fatemeh
Statement of problem: In some clinical conditions minimally invasive complete crown tooth preparations are indicated. This is especially true when gross removal of tooth structure would weaken the remaining tooth or violate the vitality of the dental pulp. Objective: The purpose of this study was to investigate the influence of (1) exposed lingual zirconia with veneered zirconia crowns, and (2) reduced lingual thickness of monolithic lithium disilicate crowns on the fracture resistance of the crowns after cyclic loading. Metal-ceramic crowns with exposed lingual metal served as controls. Materials and methods: Twenty-four maxillary central incisor crowns were fabricated in identical shape on metal testing dies in 3 groups: metal-ceramic crowns (MC, n = 8), veneered zirconia crowns (VZ, n = 8), and monolithic lithium disilicate crowns (MO, n = 8). A conservative preparation design with 0.75 mm lingual clearance was used for each crown system. All crowns were cemented to their corresponding crown preparations with self-adhesive resin cement (Multilink Automix). The crowns were subjected to 1000 cycles of thermal cycling, then cyclic loading of 111 N by means of a stainless steel ball, and 50,000 cycles of loading were applied for the fatigue test. Fatigue loading was followed by a continuously increasing compressive load, at a crosshead speed of 1 mm/min until failure. The compressive load (N) required to cause failure was recorded. Means were calculated and analyzed with one-way ANOVA and the Tukey HSD test (a= .05). Results: There was a significant difference between MO vs. MC (P = .0001), MO vs. VZ (P= .0001), and VZ vs. MC (P = .012). Conclusions: There was a significant difference in the mean fracture resistance of MC, VZ, and MO crowns in this in vitro study. The MC group recorded the highest mean fracture strength.

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