Occlusal Coverage Research Articles

Biomechanical Behavior of Lithium-Disilicate-Modified Endocrown Restorations: A Three-Dimensional Finite Element Analysis

This study aimed to assess the biomechanical behavior of endocrown-restored mandibular molars according to “margin design” and “coverage extent” using finite element analysis (FEA). Six 3D solid models were fabricated, namely, those with complete occlusal coverage: A (butt joint), B (anatomic margin); partial coverage (two mesial cusps): C (butt joint), D (anatomic margin); and partial coverage with mesial class II cavity: E (butt joint), F (anatomic margin). All models received lithium disilicate endocrowns (2.0 mm thickness and 4.0 mm central retainer cavity depth). A 300 N vertical load was applied to the occlusal surface, while a 250 N oblique load was applied at 45° to the lingual inclined planes of the buccal cusps. The maximum von Mises stress (VMS) distribution patterns were calculated for the endocrown, tooth structure, and cement layer. The VMS on the prepared teeth and cement layer showed subtle differences between the tested models under vertical loads. The anatomic margin (partial and complete coverage) exhibited a more homogeneous stress distribution and offered a more adhesive area of the tooth structure. Under oblique loading, the anatomic margin (complete and partial), except Model D, exhibited the lowest VMS in the cement layer. An anatomically based endocrown could be a promising alternative to the butt joint design, providing better-devised endocrown restorations, which could potentially yield a more benign stress dissipation.

Influence of retainer design and number of inlay boxes on the biomechanical behavior of zirconia cantilever resin bonded fixed dental prosthesis.

The development of dental adhesives with enhanced bond strength has assisted minimally invasive dentistry. The aim of this study was to evaluate the fracture load and stress distribution pattern of two retainer designs for posterior cantilever resin bonded fixed dental protheses (RBFDPs). Forty human mandibular molars were divided into two groups according to the retainer design; lingual coverage (LC) and occlusal coverage (OC) retainers. Each main group was then divided according to the number of inlay boxes (n = 10); one inlay and two inlay boxes. High translucency (3Y) zirconia was used to manufacture all restorations, and a dual-polymerizing adhesive resin cement was used for bonding. All specimens underwent 10,000 cycles of thermocycling (5-55°C), 240,000 cycles of dynamic loading (50 N, descending speed v = 30 mm/second, frequency = 1.6 Hz), and failure load test. Both one-way and two-way ANOVA tests were used to analyze the data. The four models included in the in-vitro study are part of the finite element analysis (FEA). When the restorations failed, maximal principal stress values on restorations, enamel, dentin, and luting resin were investigated. A statistically significant (p = 0.018) higher failure load was recorded for OC1 (627.00 ± 153.4 N) than the other groups; (548.0 ± 75.6 N, 521.20 ± 11.3 N, and 509.20 ± 14.9 N for LC1, LC2, and OC2, respectively). With regard to failure mode, one inlay box designs showed more favorable failure pattern than those of two inlay boxes. FEA showed higher stress magnitude transmitted to the tooth structure in models LC2 and OC2. Lingual coverage and occlusal coverage retainers are promising designs capable to withstand the normal occlusal force for cantilever RBFDP in premolar area. The use of two inlay boxes decreased the fracture load of the two retainer designs and increased the stress transmitted to the tooth and resulted in high incidence of catastrophic failure. Monolithic high translucent zirconia RBFDP could be considered as a viable treatment option to substitute missing posterior tooth, with improved esthetics and biocompatibility.

Evaluation of different designs for posterior cantilever zirconia inlay-retained fixed dental prostheses in missing tooth replacement: Stage one results with 18-month follow-up assessment

ObjectivesThis clinical study aimed to investigate the outcomes and survival rates of different variations of inlay-retained fixed dental prostheses (IR-FDPs) composed of monolithic zirconia ceramic. The IR-FDPs with a single-retainer design were used for replacing missing mandibular second premolars. The research evaluated the effectiveness and longevity of these prostheses in clinical settings. MethodsA total of 30 IR-FDPs (n = 30) were placed for 27 female patients who presented with missing mandibular second premolar teeth. For this study, the mandibular first molar was chosen as a retainer for the cantilever IR-FDPs and the study involved a random assignment of participants into three distinct groups, each comprising 10 individuals (n = 10). The criterion for the grouping was the retainer design: inlay ring (IR), lingual coverage (LC), and occlusal coverage (OC). The three groups included mesial inlay box with the same dimensions (3 mm height, 3 mm width and 2 mm depth). All IR-FDPs were manufactured using monolithic high translucent 3Y zirconia and the connector area to the cantilever pontic was adjusted to dimensions of 3 × 3 mm for all designs. The restorations were bonded using adhesive resin cement. The clinical and radiographic evaluations of the restorations were conducted for a duration of 18 months, following the modified FDI (World Dental Federation) criteria. ResultsThe restorations were observed in stage one for a period of 18 months. Only one restoration in group LC was debonded after 10 months and re-bonded. The clinical quality of all crowns and the patient's satisfaction were high. No adverse soft tissue reactions around the crowns were observed and only one abutment in group IR was endodontically treated after 12 months. ConclusionsZirconia cantilever IR-FDPs offer a viable short-term treatment option for replacing missing posterior teeth, providing esthetic and functional benefits while minimizing invasiveness. Over an 18-month observation period, these prostheses have demonstrated a remarkable survival rate of 100% and a success rate of 96.6%. These findings suggest the effectiveness and reliability of zirconia cantilever IR-FDPs as a short-term solution for replacing missing posterior teeth. Clinical significanceZirconia cantilever IR-FDPs could present a practical solution for addressing posterior tooth loss, especially in cases where implant placement is not recommended and conventional fixed dental prostheses entail excessive invasiveness.

Comparative evaluation of internal fit and marginal gap of endocrowns using lithium disilicate and polyether ether ketone materials - an in vitro study

BackgroundThe aim of the study was to investigate the effect of material and occlusal preparation design on the internal fit and marginal gap of endocrowns made of Polyether ether ketone (PEEK) and lithium disilicate.Methods32 endocrowns were fabricated on prepared mandibular molars and divided into two groups (n = 16) according to the material. Group L: lithium disilicate and Group P: PEEK. Each group was further subdivided into two subgroups (n = 8) according to the occlusal preparation design: full occlusal coverage (LF and PF) and partial occlusal coverage (LP and PP). Samples were analyzed using microcomputed tomography (µCT) with a voxel size of 6 μm to evaluate internal fit, and an optical microscope was used to evaluate the marginal gap. Data were collected, tabulated, and statistically analyzed. Numerical data were described as mean and standard deviation and compared using the ANOVA test. The level of significance was set at α P ≤ 0.05.ResultsAll groups’ internal fit and marginal gaps values were within the acceptable clinical range. However, the lithium disilicates group recorded statistically significantly higher mean internal gap values than the PEEK groups. Regardless of the material, the difference between the two occlusal designs was not statistically significant in both internal fit and marginal gap records.ConclusionWithin the limitations of this study, PEEK endocrown restorations revealed better internal fit and marginal gap than lithium disilicate endocrown restorations. The marginal and internal fit of both lithium disilicate and PEEK endocrown restorations were within the clinically acceptable range. The occlusal preparation design had no influence on the internal fit and marginal gap of the endocrown restoration.

Cantilever resin-bonded fixed dental prosthesis to substitute a single premolar: Impact of retainer design and ceramic material after dynamic loading.

To evaluate the influence of retainer design and ceramic materials on the durability of minimally invasive cantilever resin-bonded fixed dental prostheses (RBFDPs) after artificial aging. One hundred caries-free human mandibular molars were prepared as abutments for all-ceramic cantilevered fixed dental prostheses using the following retainer designs: One wing (OW), Two wings (TW), Inlay ring (IR), Lingual coverage (LC), and Occlusal coverage (OC). Two ceramic materials were used: monolithic high translucent zirconia(z) and zirconia-reinforced lithium disilicate (ZLS2) (n=10). All restorations were adhesively bonded with resin cement. The thermocycling of the specimens were performed between 5°C and 55°C for 10,000 cycles and then exposed to 240.000 cycles of dynamic loading on a chewing simulator. All surviving specimens were loaded onto the pontic until failure using a universal testing machine. The mean failure load ranged from 124.00 to 627.00 N for the zirconia groups and from 133.30 to 230.00 N for the ZLS2 groups. Regarding the materials, a significantly higher failure load was recorded in the zirconia groups than in the ZLS2 groups (P<0.001), except for OW (P=0.748). Regarding the retainer designs, a significant different failure load was recorded between the different designs except for IR and LC in the zirconia groups, IR and OC, OW and TW, and TW and LC in the ZLS2 groups (P<0.001). Zirconia IR, LC, and OC can be used as cantilever RBFDP in the premolar region. The fracture resistance of the ZLS2 design was below the normal bite force and should not be recommended as the first option.

Effect of different designs of minimally invasive cantilever resin-bonded fixed dental prostheses replacing mandibular premolar: Long-term fracture load and 3D finite element analysis.

To evaluate the fracture load and stress magnitude of different retainer designs of minimally invasive cantilever resin-bonded fixed dental prostheses (RBFDPs) after artificial aging. Fifty caries-free human mandibular molars were prepared as abutments for cantilever fixed dental prostheses using different retainer designs: one wing (OW), two wings (TW), inlay ring (IR), lingual coverage (LC), and occlusal coverage (OC). Computer-aided design and computer-aided manufacturing were used for milling the RBFDPs using fiber-reinforced composite (FRC), and the restorations were adhesively bonded. The specimens were then subjected to thermomechanical aging and loaded until failure. The 3D finite element analysis (FEA) was performed with five models of retainer designs similar to the in vitro test. Modified von Mises stress values on enamel, dentine, luting resin, and restorations were examined. Data were analyzed with Kruskal-Wallis and Mann-Whitney U tests (p<0.001). A statistically significant difference (p<0.001) was found between all groups except between IR and LC and between OW and TW designs, with the highest mean failure load detected for OC (534.70N) and the lowest detected for OW (129.80N). With regard to failure mode, OW, TW, and LC showed more incidences of favorable failure patterns than IR and OC designs. FEA showed that FRC transmitted low stresses in tooth structure and high stresses to the luting resin. LC and OC designs can be used to design cantilever RBFDPs in premolar area. IR design transmitted more stresses to the tooth structure and resulted in 30% catastrophic failure. OW and TW were below the normal occlusal force and should be carefully used.

Effect of occlusal coverage depths on the precision of 3D-printed orthognathic surgical splints

BackgroundPrecise orthognathic surgical splints are important in surgical-orthodontic treatment. This study aimed to propose a standardized protocol for three-dimensional (3D)-printed splints and assess the precision of splints with different occlusal coverage on the dentition (occlusal coverage depth, OCD), thus optimizing the design of 3D-printed splints to minimize the seemingly unavoidable systematic errors.MethodsResin models in optimal occlusion from 19 patients were selected and scanned. Intermediate splints (ISs) and final splints (FSs) with 2-mm, 3-mm, 4-mm, and 5-mm OCDs were fabricated and grouped as IS-2, IS-3, IS-4, IS-5, FS-2, FS-3, FS-4, and FS-5, respectively. The dentitions were occluded with each splint and scanned as a whole to compare with the original occlusion. Translational and rotational deviations of the lower dentition and translational deviations of the landmarks were measured.ResultsFor vertical translation, the lower dentitions translated inferiorly to the upper dentition in most of the splints, and the translation increased as OCD got larger. Vertical translations of the dentitions in 89.47% of IS-2, 68.42% of IS-3, 42.11% of IS-4, 10.53% of IS-5, 94.74% of FS-2, 63.16% of FS-3, 26.32% of FS-4, and 21.05% of FS-5 splints were below 1 mm, respectively. For pitch rotation, the lower dentitions rotated inferiorly and posteriorly in most groups, and the rotation increased as OCD got larger. Pitch rotations of the dentitions in 100% of IS-2, 89.47% of IS-3, 57.89% of IS-4, 52.63% of IS-5, 100.00% of FS-2, 78.95% of FS-3, 52.63% of FS-4, and 47.37% of FS-5 splints were below 2°, respectively. On the other hand, the transversal and sagittal translations, roll and yaw rotations of most groups were clinically acceptable (translation < 1 mm and rotation < 2°). The deviations of ISs and FSs showed no statistical significance at all levels of coverage (P > 0.05).ConclusionsA protocol was proposed to generate 3D-printed ISs and FSs with normalized basal planes and standardized OCDs. Deviations of the ISs and FSs were more evident in the vertical dimension and pitch rotation and had a tendency to increase as the OCD got larger. ISs and FSs with both 2-mm and 3-mm OCD are recommendable regarding the precision relative to clinical acceptability. However, considering the fabrication, structural stability, and clinical application, ISs and FSs with 3-mm OCD are recommended for accurate fitting.

Comparative Evaluation of Stress Acting on Abutment, Bone, and Connector of Different Designs of Acid-Etched Resin-Bonded Fixed Partial Dentures: Finite Element Analysis.

Background: Finite element analysis (FEA) is one of the best methods for evaluating the stress distribution of restorations, such as fixed partial dentures. The development of resin cement has transformed prosthesis bonding and retention properties. Resin-bonded fixed partial dentures (RBFPD) have been considered minimally invasive treatment options for the prosthetic rehabilitation of single missing teeth. Objectives: The aim of this study was to evaluate the stress load and distribution in four different designs of acid-etched RBFPDs using FEA. Materials and Methods: The designs included standard tooth preparation principles and additional features. The first premolar and first molar abutments replaced the missing second premolar. Designs 1, 2, 3, and 4 included (1) lingual wings and occlusal rests; (2) wings and proximal slices; (3) wings, rests, and grooves; and (4) wings, rests, grooves, and occlusal coverage. The prepared models were restored with RBFPDs. A load of 100 N was applied to the central groove of the pontic to simulate occlusal forces. The materials used in the models were considered to be isotropic, homogeneous, and linearly elastic. FEA was used to reveal stresses acting on the abutment, bone, and connector in all prosthesis designs. Results: The stresses transmitted to the abutment and bones were lowest for design 3, using wings, rests, and grooves. The stresses acting on the connector were the weakest in design 2. The stresses transmitted to the abutment and bone were highest in designs 1 and 4. The stresses transmitted to the connector were highest in design 3. Conclusion: The wings, rests, and grooves design is possibly the ideal and conservative tooth preparation design to receive a posterior RBFPD. This design transmits less stress to the abutments and less bone resorption in the FEA. It is most likely to be successful in the clinical provision and ensures the longevity of the prosthesis.

Short-term effect of adhesive system on clinical performance of bulk fill composite

Aim: Although bulk fill composites have been widely used as restorative material, there is no consensus regarding the best clinical protocol in terms of composite technique and adhesive system. Therefore, this clinical trial evaluated the clinical performance of bulk fill composites for class I restorations under different protocols. Methods: A randomized clinical trial including 155 class I restorations was conducted using different adhesive systems: conventional technique (phosphoric acid + conventional three-step adhesive system) (Group 1, 2 and 3); or self-etching adhesive system (Groups 4, 5 and 6). Control groups 1 and 4 were restored with conventional composite; groups 2 and 5 with low viscosity bulk fill and conventional composite as occlusal coverage; groups 3 and 6 with high viscosity bulk fill. The FDI criteria was used for clinical evaluation at baseline and after 6 months. Results: All groups showed good clinical performance. At baseline, the adhesive system did not affect postoperative hypersensitivity. After 6 months, group 5 showed a significant reduction in color and translucency; group 6 a reduction in terms of anatomical form and for postoperative sensitivity and an improvement in patient satisfaction (p&lt;0.05). Considering the same restorative technique, the use of the self-etching adhesive system showed a significant decrease in color and translucency (p&lt;0.05). Conclusion: All groups showed favorable clinical performance, and promising results were found for the conventional adhesive system and high viscosity bulk fill protocol.

Evaluation of long-term stability of curve of Spee levelled with continuous archwires in two different retention protocol

Objectives: The objectives of the study were to assess the long-term stability of the curve of Spee leveled with continuous archwire in subjects with two different retention protocols. Materials and Methods: The study sample consisted of 20 patients (mean age 18 ± 2 years) presenting with curve of Spee depth of =/&gt; 3 mm. For each subject, lateral cephalograms and dental casts were available before treatment (T1), at the end of orthodontic therapy (T2), and 1 year after the end of treatment (T3). All subjects were divided into two groups according to their retention protocol – fixed retainer group (Group-1) and Essix retainer group (Group-2). Cephalometric parameters were used to evaluate the dental movements after treatment. Curve of Spee depth was measured on standardized digital images of casts. Results: In multicomparison table, it shows that there was a statistically significant difference (P = 0.032) between Spee-T2 and Spee-T3 and there was no statistical difference (P = 0.159) between L1MP-T2 and L1MP-T3 in fixed retainer group. In Essix retainer group, no changes were observed from L1MP-T2 to L1MP-T3 and there was a non-significant difference found between Spee-T2 and Spee-T3. Conclusion: In Group-1 (fixed retainer), there is some amount of relapse or extrusion of lower incisor. In Group-2 (Essix retainer), there was not any change in the position of the lower incisor, which suggests that occlusal coverage of the Essix retainer does not allow any extrusion and retains the curve of Spee.

In-vivo-wear in composite and ceramic full mouth rehabilitations over 3 years

The aim of this study was to quantify and to compare the wear rates of premolar (PM) and molar (M) restorations of lithium disilicate ceramic (LS2) and an experimental CAD/CAM polymer (COMP) in cases of complex rehabilitations with changes in vertical dimension of occlusion (VDO). Twelve patients with severe tooth wear underwent prosthetic rehabilitation, restoring the VDO with antagonistic occlusal coverage restorations either out of LS2 (n = 6 patients, n = 16 posterior restorations/patient; N = 96 restorations/year) or COMP (n = 6 patients; n = 16 posterior restorations/patient; N = 96 restorations/year). Data was obtained by digitalization of plaster casts with a laboratory scanner at annual recalls (350 ± 86 days; 755 ± 92 days; 1102 ± 97 days). Each annual recall dataset of premolar and molar restorations (N = 192) was overlaid individually with the corresponding baseline dataset using an iterative best-fit method. Mean vertical loss of the occlusal contact areas (OCAs) was calculated for each restoration and recall time. For LS2 restorations, the mean wear rate per month over 1 year was 7.5 ± 3.4 μm (PM), 7.8 ± 2.0 μm (M), over 2 years 3.8 ± 1.6 µm (PM), 4.4 ± 1.5 µm (M), over 3 years 2.8 ± 1.3 µm (PM), 3.4 ± 1.7 µm (M). For COMP restorations, the mean wear rate per month over 1 year was 15.5 ± 8.9 μm (PM), 28.5 ± 20.2 μm (M), over 2 years 9.2 ± 5.9 µm (PM), 16.7 ± 14.9 µm (M), over 3 years 8.6 ± 5.3 µm (PM), 9.5 ± 8.0 µm (M). Three COMP restorations fractured after two years and therefore were not considered in the 3-year results. The wear rates in the LS2 group showed significant differences between premolars and molars restorations (p = 0.041; p = 0.023; p = 0.045). The wear rates in COMP group differed significantly between premolars and molars only in the first two years (p < 0.0001; p = 0.007). COMP restorations show much higher wear rates compared to LS2. The presented results suggest that with increasing time in situ, the monthly wear rates for both materials decreased over time. On the basis of this limited dataset, both LS2 and COMP restorations show reasonable clinical wear rates after 3 years follow-up. Wear of COMP restorations was higher, however prosthodontic treatment was less invasive. LS2 showed less wear, yet tooth preparation was necessary. Clinicians should balance well between necessary preparation invasiveness and long-term occlusal stability in patients with worn dentitions.

Variations in athletic performance with occlusal splint in track and field athletes: a randomized clinical trial.

Several studies have been proposed with the aim to demonstrate correlations between the dento-mandibular apparatus and the skeletal muscle system of the human body even in regions distant from the oral cavity. However, a definite conclusion cannot be drawn. The aim of this paper is to demonstrate a possible correlation between dental occlusion and sport performances in track and field athletes. Sixteen track and field athletes were enrolled for the study and were randomly divided in three groups: Untreated control group, Placebo group (with a lower plaque without occlusal coverage) and Treated group (with occlusal splint). Changes in sprint and jump performance were assessed on a weekly basis for 5 consecutive weeks, during which athletes had to wear oral devices, except for the first week of baseline, for at least 3 trainings lasting 2 hours per week . All participants performed the countermovement jump (CMJ), the drop jump (DJ), the 10m and 30m sprint tests, always on the same day on the week. No statistically significant difference resulted between Control group and Placebo group and between Control group and Treated group. However, it was possible to observe a clinical improvement of measurements obtained, especially for CMJ, 10m and 30m sprint tests. No variation neither statistical neither clinical was observed in DJ test analysis. Even if statistically it was not possible to demonstrate an improvement in sport performance, most of the athlete analyzed showed better results during training session with occlusal splint compared to athlete without occlusal splint, in countermovement jump, in 10m and 30m sprint tests.

In vivo wear of CAD-CAM composite versus lithium disilicate full coverage first-molar restorations: a pilot study over 2\xa0years

ObjectivesTo present a digital approach to measure and compare material wear behavior of antagonistic first molar restorations made of an experimental CAD/CAM composite (COMP) and lithium disilicate ceramic (LS2) in patients with reconstructed vertical dimension of occlusion (VDO) after generalized hard tissue loss.MethodsA total of 12 patients underwent complete full jaw rehabilitation with full occlusal coverage restorations made either of COMP or LS2. The first molar restorations (n = 48) were chosen for wear examination. At annual recall appointments, polyether impressions were taken, and resulting plaster casts were digitalized using a laboratory scanner. Mean observation period was 371 days for first and 769 days for second year. The resulting 96 datasets were analyzed by superimposition of 3-D datasets using an iterative best-fit method. Based on the superimposition data, the wear rates of the occlusal contact areas (OCAs) were calculated.ResultsFor antagonistic restorations made of COMP, the average wear rate was 24.8 ± 13.3 μm/month, while for LS2, it was 9.5 ± 4.3 μm/month in first year, with significant differences (p < 0.0001) between the materials. In second year, monthly wear rates decreased significantly for both materials: COMP (16.2 ± 10.7 μm/month) and LS2 (5.5 ± 3.3 μm/month). Statistical comparison between wear time showed significant differences for both materials: COMP p < 0.037 and LS2 p < 0.001. A logarithmic fit (COMP R2 = 0.081; LS2 R2 = 0.038) of the data was calculated to estimate the wear progression.SignificanceIn patients with reconstructed VDO, restorations made of LS2 show a more stable wear behavior than ones out of experimental CAD/CAM composite. In cases of complete rehabilitation, load bearing CAD/CAM-composite restorations should be critically considered for application due to their occlusal wear behavior. However, when choosing a restorative material, not only the functional occlusal stability should be taken into account but also the prospect of minimally invasive treatment with maximum preservation of natural tooth structures.

Tongue force, oral health–related quality of life, and sleep index after bruxism management with intraoral devices

Statement of problemOcclusal devices are the gold standard for managing the signs and symptoms of sleep bruxism (SB). Nevertheless, their influence on the tongue, quality of life, and sleep quality is not clear. PurposeThe purpose of this prospective clinical study was to evaluate the effects of an occlusal device on maximum tongue force, oral health–related quality of life (OHRQoL), and subjective sleep quality in individuals with SB. The correlation between maximum tongue force and tongue size and that between tongue size and dental arch size ratio were also assessed. Material and methodsSB was diagnosed by clinical examination and by using the Bruxoff device. Fifteen bruxers received occlusal devices, and another 15 received palatal devices without occlusal coverage (control). Maximum tongue force was measured by using force sensors, while the Oral Health Impact Profile (OHIP-14) was used to evaluate OHRQoL. Subjective sleep quality data were obtained by using the Pittsburgh Sleep Quality Index (PSQI). Tongue size was measured by ultrasonography, while the dental arch size was considered as the distance between the mandibular right and left first molars. After baseline measurement, participants used the devices at night, and the variables were reevaluated after 30 and 60 days. Comparisons between groups and among time points were performed with analysis of variance in a generalized linear mixed model and Tukey-Kramer test as post hoc. Correlations were analyzed by the Pearson test. ResultsMaximum tongue force decreased after wearing both devices for 30 days (P<.001). OHIP-14 and PSQI scores also reduced on day 30 (both P<.001). Maximum tongue force was not correlated with tongue size nor the ratio between tongue size and dental arch size. ConclusionIntraoral devices reduced maximum tongue force and improved OHRQoL and subjective sleep quality in bruxers.

Managing ‘last tooth in the arch syndrome’ and restoring retruded contact position

Occlusally challenging scenarios can arise during the restoration of teeth involved in the patient's Retruded Contact Position (RCP). During preparation of a tooth that provides the RCP, practitioners may encounter problems whereby they lose occlusal clearance to place an occlusal coverage restoration over the tooth in question. This may come as a shock to the practitioner, often resulting in further excessive and unplanned tooth preparation, or reduction of the opposing tooth to create occlusal clearance. This paper aims to provide a guide on how to recognize and avoid the potential pitfalls of restoring retruded contact position, through the use of proper planning and by employing appropriate management techniques. CPD/Clinical Relevance: Understanding of the relevant occlusal considerations will allow the practitioner to restore teeth involved with RCP predictably and conservatively.

Users' perceptions and preferences towards maxillary removable orthodontic retainers: a crossover randomized clinical trial.

The aim of this study was to assess, correlate, and compare users' perceptions and preference related to maxillary removable retainers. Volunteers were recruited to use four retainer types: conventional wrap-around (CWA), wrap-around with an anterior opening (OWA), "U" wrap-around (UWA), and clear thermoplastic retainer (CT). The main outcomes were the volunteers' perceptions, evaluated with a 100-mm visual analogue scale, and their preferred retainer. The retainers were used for 21 days each (washout intervals of 7 days). Nineteen volunteers (27 ± 4.53 years) were randomly divided into four groups that used the four retainers, but with a different sequence. Perceptions were evaluated immediately after the use of each retainer and the preference at the end of the research. Repeated measures ANOVA and Friedman tests with post-hoc Tukey's test (intergroup comparisons), and Pearson and Spearman analyses (correlations between perceptions) were applied. The WA retainers did not significantly differ among themselves. The CT was rated significantly worse in speech (p ≤ 0.001), discomfort (p < 0.001), and occlusal interference (p < 0.001), and did not significantly differ from the others in esthetics. Users preferred significant more the WA retainers in comparison with the CT retainers. The occlusal interference caused by the CT was positively correlated to other perceptions, such as changes in speech and discomfort. WA retainers presented similar preference and perceptions, but were significantly better than the CT. The CT occlusal coverage appeared to be the primary cause of its rejection.

The iatrogenic anterior open bite; a potential side-effect of thermoplastic orthodontic retainers

Abstract: Thermoplastic orthodontic retainers are popular with both patients and clinicians. Tooth coverage provides retention of orthodontic alignment, particularly in the lower labial segment, and their aesthetics are improved in comparison with more traditional acrylic and wire varieties. Iatrogenic side-effects are possible if the design is inadequate. Lack of coverage of terminal molars can allow overeruption, causing an anterior open bite. This report describes an anterior open bite caused by an inadequate thermoplastic retainer and management using a Hawley type retainer to improve the open bite which had arisen. CPD/Clinical Relevance: The provision of orthodontics has grown and with this the potential for detrimental occlusal effects due to inadequate extension of occlusal coverage appliances such as retainers and clear aligners.

Residents' journal review

Residents' journal review

Postural changes in orthodontic patients treated with clear aligners: A rasterstereographic study

BackgroundCorrelation between malocclusions and body posture has been discussed in the last decades, but there is still a lack of consensus in existing literature. Rasterstereography allows tridimensional reconstruction of the spine, starting from the back surface analysis. So far studies which tested modifications of rasterstereographic parameters during orthodontic treatment, comparing with those obtained from untreated control group, are not available. Clear aligner treatment produces alteration of vertical height due to the occlusal coverage and, subsequently, a stimulation of periodontal receptors which causes an inhibition of the jaw closing muscles and, hypothetically, changes in mandibular posture. ObjectivesEvaluate possible correlations between orthodontic treatment and posture. Materials and methodsRasterstereographic values of 15 untreated patients and of 15 patients treated with clear aligners were compared at baseline, after 1, 3 and 6 months. Rasterstereographic parameters considered were the following: the kyphotic angle, the lordotic angle, the upper thoracic inclination, and the pelvic inclination. ResultsCorrelations between Kyphosis Angle, Upper Toracic Inclination and Pelvic Inclination and body posture were found after 6 months of treatment with clear aligners. ConclusionsOcclusal coverage caused by aligners could influence body posture not only for upper spine sections but also lower spine sections.

Effect of placing intentionally high restorations: Randomized clinical trial

ObjectiveThe aim of this study was to examine the behavior of posterior teeth restored with single-tooth restorations with intentionally high occlusal contacts. MethodsConsent was obtained from 17 patients who were seen a total of 5 times over 3.5 years. The restorations placed were all full occlusal coverage gold restorations. Tooth mobility was recorded using the Periotest device and tooth movement was determined from impressions and 3D imaging. Patients were randomly assigned into two groups, the control group which received restorations with no intentional increase of the occlusal vertical dimension; or the treatment group where they received intentionally high restorations in 0.5mm supraocclusion. ResultsStatistical analysis showed no significant difference in mobility between visits for both the control and the treatment groups while a significant dependency and difference in tooth movement was observed between the subjects of the two groups. Most patients from the treatment group reported discomfort but no pain for the first 7–10 days after the restoration was fitted, which subsided over a period of couple of weeks. At review, 3 years later, no mobility or additional movement was observed. ConclusionsCementation of an intentionally high single-tooth restoration causes no increase in tooth mobility while occlusal adaptation re-establishes and restores the occlusal plane.