Effect of occlusal splint therapy on maximum bite force in individuals with moderate to severe attrition of teeth

ObjectiveThe purpose of the pilot study was to determine the effect of restoring lost occlusal vertical dimension (OVD) due to attrition on maximum bite force in humans.MethodologyA total of 124 subjects in age range of 25–40 years, with moderate to severe attrition, having full complement of teeth were screened according to inclusion and exclusion criteria. After consent, occlusal vertical dimension was assessed by employing mechanical and physiological methods in the experimental group and a maxillary canine guided hard splint was fabricated for each subjects fulfilling inclusion criteria and with positive consent (78). Bite force in experimental group was measured before, immediately after delivery of splint and subsequently at an interval of four, eight, and twelve weeks. Due loss during follow up, only 50 subjects could be available for bite force recording till 12 weeks. Bite force of age, gender, height and weight matched controls with no signs of attrition was also measured for comparison.ResultsBite force of the experimental group was found to be significantly less than the matched controls (P = 0.000) initially. After delivery of splint, bite force values increased progressively till twelve weeks. However comparison of bite force values of experimental group with control group showed no significant difference at end of eight (P = 0.008) and twelve weeks (P = 0.162).ConclusionIt was concluded that maximum bite force increases with restoration of lost vertical using splint therapy. A time period of 8–12 weeks is required to restore the maximum bite force value approximately similar to matched controls.     

Two-year follow-up of changes in bite force and occlusal contact area after intraoral vertical ramus osteotomy with and without Le Fort I osteotomy

This study was performed to examine the longitudinal changes in bite force and occlusal contact area after mandibular setback surgery via intraoral vertical ramus osteotomy (IVRO). Patients with mandibular prognathism who underwent IVRO (surgical group: 39 men and 39 women) were compared with subjects with class I skeletal and dental relationships (control group; 32 men and 35 women). The surgical group was divided into two subgroups: 1-jaw surgery (n = 30) and 2-jaw surgery (n = 48). Bite force and contact area were measured in maximum intercuspation with the Dental Prescale System before treatment, within 1 month before surgery, and at 1, 3, 6, 9, 12, and 24 months postsurgery. A linear mixed model was used to investigate the time-dependent changes and associated factors. Bite force and contact area decreased during presurgical orthodontic treatment, were minimal at 1 month postsurgery, and increased gradually thereafter. The 1-jaw and 2-jaw subgroups showed no significant differences in bite force. The time-dependent changes in bite force were significantly different according to the contact area (P < 0.05). The results of this study suggest that bite force and occlusal contact area gradually increase throughout the postsurgical evaluation period. Increasing the occlusal contact area may be essential for improving bite force after surgery.     

Does pain in the masseter and anterior temporal muscles influence maximal bite force?

ObjectiveThe aim of this study was to evaluate changes in pain and muscle force, and the relationship between them, in patients with muscle pain and bruxism, prior to and after treatment.MethodsThirty women with bruxism and myofascial pain (Ia) were included in this study. Sleep bruxism diagnosis was made based on clinical diagnostic criteria, and awake bruxism diagnosis was made by patient questionnaires and the presence of tooth wear. The diagnosis of myofascial pain was established according to the Research Diagnostic Criteria for Temporomandibular Disorders (RDC-TMD). Dentulous or partially edentulous patients (rehabilitated with conventional fixed prostheses) were included in the study according to the inclusion and exclusion criteria. The pain treatment protocol included occlusal splints, patient education, and physiotherapy for 30 days. Bite force was measured using a dynamometer at the central incisor and the first molar regions on both sides. The exams were performed at baseline, after 7 days, and 30 days after treatment. The Wilcoxon test was used to compare patient pain level response among the periods analyzed in the study. Bite force data were submitted to two-way repeated-measures ANOVA, followed by the Tukey HSD test (p < 0.05). A simple regression analysis was performed to verify the relation between pain level and bite force.ResultsResults revealed that there was a statistical difference in pain level over time for both muscles and sides (p < 0.01). In the molar region, the bite force exhibited significantly higher values after 30 days of treatment, when compared with the baseline (p < 0.001). There was a correlation between pain level and bite force only for the temporal muscle in all periods analyzed (p < 0.05). There was no strong correlation in the response level points to support the association of pain and bite force.ConclusionsPain level decreased and bite force increased in the molar region after treatment. No strong correlation or dispersion in the relationship between pain levels and bite force was seen in women with myofascial pain and bruxism.     

Making three-dimensional Monson's sphere using virtual dental models

ObjectivesThe Monson's sphere and curve of Wilson can be used as reference for prosthetic reconstructions or orthodontic treatments. This study aimed to generate and measure the three-dimensional (3-D) Monson's sphere and curve of Wilson using virtual dental models and custom software.MethodsMandibular dental casts from 79 young adults of Korean descent were scanned and rendered as virtual dental models using a 3-D digitizing scanner. 26 landmarks were digitized on the virtual dental models using a custom made software program. The Monson's sphere was estimated by fitting a sphere to the cusp tips using a least-squares method. Two curves of Wilson were generated by finding the intersecting circle between the Monson's sphere and two vertical planes orthogonal to a virtual occlusal plane. Non-parametric Mann–Whitney and Kruskal–Wallis tests were performed to test for difference between sex and in cusp number within tooth position.ResultsThe mean radius of Monson's sphere was 110.89 ± 25.75 mm. There were significant differences between males and females in all measurements taken (p < 0.01), within 16.87–17.27 mm. Furthermore, morphological variation derived from variability in cusp number in the second premolar and second molar were not found to influence occlusal curvature (p > 0.05).ConclusionsThis study describes a best-fit algorithm for generating 3-D Monson's sphere using occlusal curves quantified from virtual dental models. The radius of Monson's sphere in Korean subjects was greater than the original four-inch value suggested by Monson.Clinical significanceThe Monson's sphere and curve of Wilson can be used as a reference for prosthetic reconstruction and orthodontic treatment. The data found in this study may be applied to improve dental treatment results.     

Influence of mandibular residual ridge resorption on objective masticatory measures of lingualized and fully bilateral balanced denture articulation

PurposeTo assess the influence of mandibular residual ridge resorption (RRR) on objective masticatory measures of two occlusal schemes: lingualized occlusion (LO) and fully bilateral balanced articulation (FBBA).MethodsThe enrolled patients (n = 22) were randomly allocated one set of complete dentures with either LO or FBBA. Maximum occlusal force, masticatory performance (by the MPI), and mandibular movements were measured at 3- and 6-month follow-ups. Mandibular RRR was assessed as the sum of the mandibular bone height at the midline, first premolar region, and least vertical height region, and from the mental foramen to the alveolar crest, measured on panoramic radiographs; the treatment groups were subclassified into severe or moderate RRR subgroups by the value of the sum of individual measurements.ResultsSignificant differences were observed in the between-subgroup comparisons (Kruskal–Wallis test) of the MPI (3 months, p = 0.01; 6 months, p = 0.04) and linear deviation from intercuspal position (anterior–posterior: 6 months, p = 0.01; inferior–superior: 3 months, p = 0.008; 6 months, p = 0.02). The patients with severe RRR in the FBBA group showed a significant decrease in the MPI and increase in linear inferior deviation from intercuspal position at 3 months (post hoc comparison) as well as a significant increase in the linear posterior and inferior deviation from intercuspal position at 6 months.ConclusionsLO is the preferable occlusal scheme for patients with severe RRR. (This trial has been registered at http://clinicaltrials.gov/ct2/show/NCT00959530.)     

Clinical interpretation of a masticatory normative indicator analysis of masticatory function in subjects with different occlusal and prosthodontic status

ObjectivesTo analyse the masticatory function of subjects characterised by different occlusal and prosthodontic status. Using Optosil^® as a test food, the masticatory normative indicator (MNI_OPT) was used to differentiate between sufficient (‘normal’) and impaired masticatory function.MethodsOutcomes of occlusal force and masticatory tests were aggregated from three earlier studies dealing with four denture groups and three natural dentition groups. The four denture groups had a complete removable dental prosthesis in the upper jaw, and displayed one of the four following lower jaw prosthodontic rehabilitations: (i) complete removable dental prosthesis on a low mandible; (ii) complete removable dental prosthesis on a higher mandible; (iii) overdenture on natural roots; and (iv) overdenture on dental implants. The three natural dentition groups were: (i) shortened dental arch; (ii) complete dentition in older participants, and (iii) complete dentition in younger participants. All participants were women. They performed the same tests twice, and outcomes were averaged.ResultsA MNI_OPT value of 3.68 mm was determined from the participants with complete natural dentitions. Applying the MNI_OPT to the participants in the denture groups pointed at a considerable chance for impaired masticatory function, except for participants in the overdenture – implants group. The four denture groups compensated for reduced masticatory efficiency by increased number of masticatory cycles and prolonged mastication time until ‘swallowing’. Nevertheless, they also ‘swallowed’ larger particles compared to the complete dentition group.Clinical significanceFor a given patient or for a group of subjects with specific dental conditions, MNI enables to discriminate between a sufficient (‘normal’) and an impaired masticatory function.     

Effect of implant‐supported prosthesis on the bite force and masticatory efficiency in subjects with shortened dental arches

The aim of the study was to assess changes in bite force and masticatory efficiency in shortened dental arch (SDA) subjects rehabilitated with implant‐supported restoration for 1st molar. Ten SDA subjects with bilaterally missing mandibular molars (experimental group) were recruited. In each subject, one tapered threaded implant was placed bilaterally in 1st mandibular molar region and restored. Masticatory efficiency was evaluated objectively by measuring the released dye from chewed raw carrots, with a ‘spectrophotometer’ at 530 nm preoperatively and at 3 months after restoration. Bite force was evaluated using ‘bite force measuring appliance’ preoperatively, at 6 weeks and at 3 months after restoration. Ten completely dentate‐matched subjects (in terms of age, sex, height and weight) acted as control. The results revealed that as compared with the control group, the experimental group showed significantly less (P < 0·05) mean maximum bite force at pre‐restoration and at 6 weeks after restoration. Although at 3 months the mean maximum bite force value was less than the control group but the mean difference was statistically insignificant. The mean difference of masticatory efficiency between control and experimental group was statistically significant (P < 0·05) before restoration, but was statistically insignificant at 3 months after restoration. Thus it was concluded that after the restoration of mandibular arch with implant‐supported prosthesis, both bite force and masticatory efficiency of all SDA subjects increased and were comparable to that of matched completely dentate subjects after 3 months.     

Dental image replacement on cone beam computed tomography with three-dimensional optical scanning of a dental cast,occlusal bite,or bite tray impression

The goal of the present study was to compare the accuracy of dental image replacement on a cone beam computed tomography (CBCT) image using digital image data from three-dimensional (3D) optical scanning of a dental cast, occlusal bite, and bite tray impression. A Bracket Typodont dental model was used. CBCT of the dental model was performed and the data were converted to stereolithography (STL) format. Three experimental materials, a dental cast, occlusal bite, and bite tray impression, were optically scanned in 3D. STL files converted from the CBCT of the Typodont model and the 3D optical-scanned STL files of the study materials were image-registered. The error range of each methodology was measured and compared with a 3D optical scan of the Typodont. For the three materials, the smallest error observed was 0.099 ± 0.114 mm (mean error ± standard deviation) for registering the 3D optical scan image of the dental cast onto the CBCT dental image. Although producing a dental cast can be laborious, the study results indicate that it is the preferred method. In addition, an occlusal bite is recommended when bite impression materials are used.     

Masticatory efficiency and bite force in individuals with normal occlusion

ObjectiveThe aim of the study was to evaluate and correlate masticatory efficiency (ME) and maximum bite force (MBF) in adult individuals of both genders with normal occlusion.DesignThe study was conducted in a university research centre. ME and MBF were evaluated in 55 adults (27 men and 28 women) with normal occlusion. All subjects chewed four fuchsin capsules (two on the right and two on the left molar region) for 15 chewing cycles with a 3-min interval between capsules. The concentration of fuchsin in the capsules was determined by spectrophotometry and stratified by gender and chewing side. Bite force (BF) was measured three times on both the left and right molars; the highest value of the three measurements on each side was taken as the MBF.ResultsME was higher in women (right side, 1.17 ± 016 μg/mL; left side, 1.20 ± 0.15 μg/mL) than in men (right side, 0.92 ± 0.24 μg/mL; left side, 0.89 ± 0.24 μg/mL). The MBF was higher in men (right side, 632 ± 174 N; left side, 627 ± 170 N) compared with women (right side, 427 ± 140 N; left side, 420 ± 112 N). No significant differences in chewing efficiency and BF were found between sides for both genders.ConclusionsWomen showed the highest ME, while men had the highest MBF, with no correlation between these two parameters among genders.     

Investigation of predictors affecting food mixing ability in mandibulectomy and/or glossectomy patients

PurposeSeveral previous reports have described factors that affect masticatory function. However, there are no known predictors that affect the food mixing ability of the masticatory function, and it has been impossible to predict masticatory function in mandibulectomy and/or glossectomy patients. The purpose of the present study was to develop a numerical formula that could predict the food mixing ability of the masticatory function among mandibulectomy and/or glossectomy patients. The null hypothesis of the study was that five predictors, namely mandibulectomy, mandibular continuity, number of residual mandibular teeth, occlusal units and tongue movement score, were unable to account for the mixing ability index (MAI) in mandibulectomy and/or glossectomy patients.MethodsThe subjects were 20 patients who had undergone mandibulectomy and/or glossectomy. The above-described five predictors were assessed. Tongue movement was evaluated with a tongue movement test and the MAI was evaluated with a mixing ability test. Multiple regression analysis was used to examine whether the five predictors affected the MAI after prosthetic treatment.ResultsA regression equation was determined for the five predictors (R² = 0.83; adjusted R² = 0.77; p < 0.001).ConclusionThe obtained regression equation could successfully account for the MAI in mandibulectomy and/or glossectomy patients.     

The influence of vertical dimension of occlusion changes on the electroencephalograms of complete denture wearers

PurposeThe present study was conducted to identify how changes in the vertical dimension of occlusion (VDO) affect the sensory perception and activity of the brain in complete denture wearers using an electroencephalogram (EEG).MethodsSubjects were 21 individuals wearing complete dentures who regularly visited the Division of Prosthodontics at Tsurumi University Dental Hospital for checkups (12 males and 9 females, average age: 76.6). Based on their original dentures, two duplicate dentures with different VDO (−3 mm and +5 mm) were fabricated. EEG activity and occlusal force were measured before and after gum chewing with each denture in all subjects. Negative indicator scores for psychological conditions and stable neuronal activity (Dα) were calculated using EEG data. Statistical analysis was performed using the Wilcoxon test to compare changes in the sensory perception, activity of the brain, and occlusal force (α = 0.05).ResultsAfter gum chewing with the +5-mm denture, a significant increase was observed in the negative indicator score (p < 0.05). No significant difference was found in the Dα values before and after gum chewing with any of the dentures (p > 0.05). A significant decrease was observed in the occlusal force between the original denture and the −3-mm denture (p < 0.05).ConclusionPsychological condition and occlusal force were influenced by immediate changes in the VDO of the complete denture.     

Effect of denture adhesives on oral moisture: A multicenter randomized controlled trial

PurposeThe purpose of this study was to investigate the effect of denture adhesives on oral moisture in a 10-center parallel randomized clinical trial.MethodsTwo hundred edentulous subjects wearing complete dentures were allocated into three groups: cream-type adhesive, powder-type adhesive and control groups. The adhesives (and saline solution in the control group) were applied to the mucosal surface of the dentures for 4 days, and baseline data and data after the intervention for eight meals over 4 days were obtained. For the main outcome, oral moisture was measured with a moisture checking device. Secondary outcomes were denture satisfaction, masticatory performance, denture retention, and occlusal force. In addition to between-group and within-group comparisons of oral moisture, investigations for secondary outcomes were undertaken in subgroups classified according to the degree of oral moisture at baseline (normal subgroup and dry mouth subgroup). Intention-to-treat analysis was also performed.ResultsBetween-group and within-group comparisons of oral moisture showed no significant differences. The cream-type and powder-type denture adhesives were significantly effective in the dry mouth group for denture satisfaction ratings of ability to masticate, stability, retention, and comfort of mandibular dentures (p < 0.05). The masticatory performance and retentive force of the dry mouth denture adhesive using groups were significantly improved after intervention (p < 0.05).ConclusionsThe oral moisture of complete denture wearers was not influenced by the use of denture adhesives. Our findings showed that denture adhesives improved subjective denture satisfaction, masticatory performance, and retention for complete denture patients with oral dryness.     

Prevalence of malocclusions and orthodontic treatment need in 8- to 12-year-old schoolchildren in Casablanca,Morocco

ObjectivesThe purpose of this work was to evaluate the prevalence of malocclusions and orthodontic treatment need among schoolchildren in Casablanca, Morocco.Materials and methodsA sample of 1000 children aged between 8 and 12 years, with no history of orthodontic treatment, was chosen at random in state schools in different administrative areas of the city of Casablanca. Data was registered using the method of Bjork et al. (1964). Orthodontic treatment need was assessed with the index used by the Swedish National Board of Health (SweNBH).ResultsWe found Angle Class I malocclusions in 61.4%, Class II in 24%, Class III in 10% and an indeterminate molar class with one or more missing molars in 4.6% of the children. Overjet was 1–4 mm in 63.8%, 4–6 mm in 17.2% and >6 mm in 10%. Bite was normal in 65.4%, 23.6% presented an overbite greater than 4 mm, 1.7% an anterior open bite ≤3 mm, 1.2% an anterior open bite >3 mm and 0.2% a bilateral open bite. Half of the sample presented anterior crowding, while only 2.5% presented posterior crowding. In all, 84.2% of the subjects needed some orthodontic treatment, and 15.8% needed no treatment. No statistically significant difference was found between sex or age and orthodontic treatment need (P>0.05).ConclusionsThis study found a strong need for orthodontic treatment, confirming the utility of implementing a programme of bucco-dental prevention and screening for malocclusion.     

Optimization of jaw muscle activity and fine motor control during repeated biting tasks

ObjectiveTo investigate if repeated holding and splitting of food morsel change the variability of force and jaw muscle activity in participants with natural dentition.MethodsTwenty healthy volunteers (mean age = 26.2 ± 3.9 years) participated in a single session divided into six series. Each series consisted of ten trials of a standardized behavioural task (total 60 trials) involving holding and splitting a flat-faced tablet (8 mm, 180 mg) placed on a bite force transducer with the anterior teeth. The hold and split forces along with the electromyographic (EMG) activity of the left and right masseter (MAL and MAR), left anterior temporalis (TAL) and digastric (DIG) muscles were recorded. A series (ten trials) of natural biting tasks was also performed before and after the six series of the behavioural task.ResultsThe mean hold force (P < 0.001) but not the mean split force (P = 0.590) showed significant effect of number of series. No significant effect of series was seen on the variability of hold and split force and the EMG activity except for the variability of EMG activity for MAL during the hold phase (P = 0.021) and DIG during the split phase (P < 0.001). The behavioural task had no effect on the EMG activity of the natural biting task.ConclusionThere was no evident optimization of jaw motor function in terms of reduction in the variability of bite force values and muscle activity, when this simple task was repeated up to sixty times in participants with normal intact periodontium.     

Fracture strength of CAD/CAM composite and composite-ceramic occlusal veneers

PurposeTo determine the effect of material type and restoration thickness on the fracture strength of posterior occlusal veneers made from computer-milled composite (Paradigm MZ100) and composite-ceramic (Lava Ultimate) materials.Methods60 maxillary molars were prepared and restored with CAD/CAM occlusal veneer restorations fabricated from either Paradigm MZ100 or Lava Ultimate blocks at minimal occlusal thicknesses of 0.3, 0.6, and 1.0 mm. Restorations were adhesively bonded and subjected to vertical compressive loading. The maximum force at fracture and mode of failure were recorded. 2-Way ANOVA was used to identify any statistically significant relationships between fracture strength and material type or thickness. Spearman's rank correlation coefficient was used to analyze mode of failure with regard to fracture strength.ResultsThe average maximum loads (N) at fracture for the Paradigm MZ100 groups were 1620 ± 433, 1830 ± 501, and 2027 ± 704 for the material thicknesses of 0.3, 0.6, and 1.0 mm, respectively. The Lava Ultimate groups fractured at slightly higher loads (N) of 2078 ± 605, 2141 ± 473, and 2115 ± 462 at the respective 0.3, 0.6, and 1.0 mm thickness.Statistical analyses revealed that, while no significant difference existed among the various restoration thicknesses in terms of fracture strength (P > 0.05), the material type was found to be influential (P = 0.04). The maximum load at fracture (N) for Lava Ultimate averaged over all thicknesses (2111 ± 500) was significantly higher than that of the Paradigm MZ100 (1826 ± 564). No correlation between mode of failure and fracture strength was found.ConclusionsUnder the conditions of this study, the maximal loads at fracture for these “non-ceramic” occlusal veneer restorations were found to be higher than human masticatory forces. Occlusal veneers made from the two materials tested are likely to survive occlusal forces regardless of restoration thickness, with those fabricated from the composite-ceramic hybrid material being more likely to survive heavier loads.     

Changes in dental and basal archforms with preformed and customized archwires during orthodontic treatment

ObjectivesTo evaluate changes to the dental and dentoalveolar (WALA Ridge) arch widths with preformed and customized archwires during orthodontic treatment.Methods20 patients treated with preformed archwires and 20 treated with customized archwires were recruited. Pre-treatment (T1) and post-treatment (T2) mandibular casts were used to determine the changes in dental and dentoalveolar arch width measured at the canine, premolar and molar areas. Ratios of transverse dental to dentoalveolar movements were also calculated. Results were compared to an untreated control group with mandibular casts taken at two comparable time points. Data were analyzed using ANOVA and t-test.ResultsSignificant changes in dental and dentoalveolar arch width were found with the preformed archwire group when compared to the control (p < 0.05). However, no significant changes in dental and dentoalveolar arch width were found with the customized archwire group compared to the control. Significant correlations were found between the dental and dentoalveolar arch widths. However, the ratios of dental to dentoalveolar transverse change differed between the groups and indicated that the types of movements were contrasting between the preformed and custom arch forms as each expanded the dental arches.ConclusionsThe WALA Ridge is a stable landmark when archwires are customized or shaped to the WALA Ridge. Changes in the WALA Ridge are expected when preformed archwires are used which do not conform to the patient's dentoalveolar arch width defined by the WALA Ridge. This is probably accounted for by the different types of tipping combined with extrusion that both methods employ.     

Camouflage treatment in skeletal Class III cases combined with severe crowding by extraction of four premolars

PurposeTo evaluate the changes in dentoskeletal structures and profile after extraction of four premolars in adult skeletal Class III borderline cases.Subjects and methodsThirteen Chinese patients (mean age was 22.0 ± 4.5 years) with skeletal Class III malocclusions and severe crowding in the upper arch were included in the study. These cases were diagnosed to be in the borderline surgical-orthodontic range but refused surgical treatments. All of them were treated by extraction of four premolars and standard edgewise technique. Lateral cephalometric radiographs taken at the start and end of treatment were analysed. Twenty-six cephalometric variables were calculated and paired t-tests were performed to assess the statistical significance of the treatment effects.ResultsNo significant changes were noted in the skeletal parameters (P ≥ 0.05). Regarding the dental parameters, the L1-MP angle decreased by 8.4°, the U1-L1 angle increased by 11.7° (P < 0.01), the L1-NB angle decreased by 10.1° and the L1-NB distance decreased by 5.2 mm (P < 0.01). The soft tissue parameters of Li-E, Li-H and Li-RL2 distance decreased by 3.3 mm, 3.3 mm and 4.5 mm, respectively (P < 0.01). All the patients finished with favorable occlusion and a straight profile.ConclusionsThe orthodontic camouflage by extraction of four premolars provides a viable treatment alternative for borderline skeletal Class III cases to achieve satisfying occlusal relationship and improve facial esthetics.     

Monolithic crowns fracture analysis: The effect of material properties,cusp angle and crown thickness

ObjectivesThis study aimed to investigate the collective influence of material properties and design parameters on the fracture behavior of monolithic dental crowns.MethodsThree-dimensional (3D) models (N = 90) with different combinations of design parameters (thickness, cusp angle and occlusal notch geometry) and material type (lithium disilicate, feldspar ceramic, zirconia, hybrid resin ceramic and hybrid polymer-infiltrated ceramic) were developed for the failure analysis using extended finite element method (XFEM) to identify the stress distribution, crack initiation load, fracture surface area and fracture pattern. Analytical formulation, in vitro fracture tests and fractographic analysis of dedicated models were also performed to validate the findings of the XFEM simulation.ResultsFor all material types considered, crowns with a sharp occlusal notch design had a significantly lower fracture resistance against occlusal loading. In most of the models, greater crown thickness and cusp angle resulted in a higher crack initiation load. However, the effect of cusp angle was dominant when the angle was in the low range of 50° for which increasing thickness did not enhance the crack initiation load.SignificanceComparing the critical load of crack initiation for different models with the maximum biting force revealed that for the studied monolithic materials excluding zirconia, a design with a rounded occlusal notch, 70° cusp angle and medium thickness (1.5 mm occlusal) is an optimum combination of design parameters in terms of tooth conservation and fracture resistance. Zirconia crowns exhibited sufficient strength for a more conservative design with less thickness (1.05 mm occlusal) and sharper cusp angle (60°).     

The association between occlusal factors and noncarious cervical lesions: A systematic review

ObjectivesThis study aimed to systematically review the scientific evidence for the association between noncarious cervical lesions (NCCL) and occlusal risk factors (ORF) [occlusal interferences in excursive movements; occlusal force; premature contacts; type of guidance; skid of centric occlusion to maximum intercuspidation] in adults.SourcesPubmed, Web of Science, Cochrane, Lilacs, Clinical Trials, National Research Register and National Institute for Health were searched.Study selectionFrom 1082 potentially eligible studies, 106 were selected for full text analysis. Two independent reviewers (Kappa = 0.8; p < 0.001) selected the studies, abstracted information and assessed quality based on standardised scales. Six cross-sectional, two case-controls and one clinical trial were included. Several occlusal variables were analysed among the studies, but there was no standardisation of the units used in the analysis of occlusal factors. The majority of studies did not find significant associations between NCCL and ORF. Three studies found associations between NCCL and some variables (occlusal contact area, right canine guidance, premature contacts in centric relation and working side) (p < 0.05). The methodological quality varied across studies, and there was high heterogeneity among them.ConclusionCurrent scientific evidence does not support an association between ORF and NCCL. Further prospective studies with standardised methods are vital to strengthen the evidence.Clinical significanceUnderstanding the risk factors for NCCL is important to control the causes and to help the dentist choose the best approach for the patient. The evidence does not support intervention to alter some occlusal factors for the prevention or control of the progression of NCCL.     

The effect of occlusal loading on cervical gap deformation: A 3D finite element analysis

ObjectivesSecondary caries can be accelerated by hydrodynamic flow in a gap between the tooth and restorative material. This study investigated whether occlusal loading can lead to increased hydrodynamic flow by deforming a gap between tooth and restorative material.Methods3D finite element analysis was employed to model a molar containing a restoration with an interfacial gap. The model was loaded using direct cusp-to-restoration contact and using a rubber tube model simulating a food bolus. The object exerting pressure was moved across the molar from buccal to lingual side. The applied forces were 50, 100, 200 and 400 N. The elastic modulus of the restoration material was varied between 5, 10, 15.9 and 25 GPa to resemble different kinds of composite. The primary outcome parameter was the volume of the gap under occlusal pressure.ResultsOcclusal loading resulted in deformation of the gap area. Maximum deformation was seen when loading was applied in the middle of the restoration. Higher forces and lower restoration stiffness led to more deformation of the gap. Maximum deformation with a force of 100 N and composite modulus of 15.9 GPa was −0.0083 mm³ (1.12%).SignificanceDeformation of the gap between tooth and restorative material could lead to increased hydrodynamic flow and faster secondary caries lesion formation. The measured deformation is small. Further research needs to show whether gap compression through occlusal loading affects secondary caries formation to a clinically relevant degree.