Pattern of maxillary and mandibular proximal enamel thickness at the contact area of the permanent dentition from first molar to first molar

Predictors of survival of large non-occlusal non-incisal glass-ionomer restorations in older adults

PURPOSE

This study aimed to investigate the predictors of survival of non-occlusal non-incisal glass-ionomer restorations as a surrogate for root surface restorations among older adults.

METHODS

In a retrospective cohort analysis using the University of Iowa College of Dentistry electronic dental records, we included 721 patients aged 65+ who received 2+ surface non-occlusal non-incisal glass ionomer restorations placed from January 2005 - December 2011. Restorations were followed until September 2017 or until they were deemed to have failed.

RESULTS

At baseline, participants' mean age was 77.6 ± 8.2 years, and 45.8% were females. Most patients were self-pay (65.2%). Most restorations were placed by residents and dental students (82.7%) and included only two surfaces (95.6%). About half (49.1%) failed during follow-up, with a median survival time of 3.7 years. The time ratio for lower incisors compared to other teeth was 0.6 (p = .006), for three-and-four-surface restorations compared to two was 0.7 (p = .007), for faculty as providers compared to residents and students was 1.4 (p = .039), and for the Geriatric & Special Needs Clinic compared to others was 0.8 (p = .013). Time ratios less than one indicate association with shorter durations for restorations, and time ratios greater than one indicate association with longer durations for restorations.

CONCLUSION

Tooth type, number of restored surfaces, provider type, and clinic were all significant factors associated with survival of these restorations.

Assessment of interproximal enamel reduction planned by the digital set-up of a customized lingual orthodontic appliance: A comparison cohort study

Objectives

Interproximal enamel reduction (IER), commonly known as stripping, is a frequently used technique in orthodontic treatment to address issues related to arch length discrepancies and tooth size discrepancies (TSD). The use of digital set-up allows for precise prediction of the amount of IER required. TSD occurs when the sizes of maxillary and mandibular teeth are not in proportion to each other. This study aims to evaluate and compare the suggested IER values generated by the digital set-up of a customized lingual orthodontic appliance in both upper and lower arches, across sextants, and among different teeth concerning TSD.

Materials and methods

We analyzed suggested IER values from 809 cases. The statistical analysis was divided into two parts: part 1 focused on the number of stripped surfaces, and part 2 assessed the quantity of enamel removed. Comparisons were made between upper and lower arches, sextants, and teeth using the Friedman test, followed by pairwise Wilcoxon tests with Bonferroni correction.

Results

The study found that mandibular and frontal stripping were more frequently suggested than maxillary and posterior stripping. Lower canines were the teeth most commonly recommended for stripping, followed by upper incisors.

Conclusion

Within the scope and limits of this cohort study, we conclude that, in general, more IER is required in the mandible as compared to the maxilla. Particularly in the anterior sextants, IER might be necessary to achieve optimal alignment and occlusion.

Novel Technique of Interproximal Enamel Reduction Based on Computer-Aided Navigation Technique-An In Vitro Study

The aim of this study was to analyze and compare the accuracy of a novel interproximal enamel reduction (IPR) technique based on a computer-aided static navigation technique with respect to a conventional free-hand-based technique for interproximal enamel reduction. Twenty anatomical-based experimental cast models of polyurethane were randomly distributed into the following IPR techniques: IPR technique based on computer-aided static navigation technique (n = 10) (GI) for Group A and conventional free-hand-based technique for the IPR (n = 10) (FHT) for Group B. The anatomical-based experimental cast models of polyurethane randomly assigned to the GI study group were submitted for a preoperative 3D intraoral surface scan; then, datasets were uploaded into 3D implant-planning software to design virtual templates for the interproximal enamel reduction technique. Afterward, the anatomical-based experimental cast models of polyurethane of both GI and FHT study groups were subjected to a postoperative digital impression by a 3D intraoral surface scan to compare the accuracy of the interproximal enamel reduction techniques at the buccal (mm), lingual/palatal (mm), and angular (◦) levels using the Student t-test. Statistically significant differences between the interproximal enamel reduction technique based on the computer-aided static navigation technique and the conventional free-hand-based technique for the interproximal enamel reduction at the buccal (p = 0.0008) and lingual/palatal (p < 0.0001) levels; however, no statistically significant differences were shown at the angular level (p = 0.1042). The interproximal enamel reduction technique based on computer-aided static navigation technique was more accurate than the conventional free-hand-based technique for interproximal enamel reduction.

Digital workflow for proximal adjustment of teeth adjacent to implant-supported fixed restorations using a predesigned computer-aided grinding guide

Clinically, the proximal surfaces of teeth adjacent to an implant restoration usually need to be adjusted to build a preferable adjacency relationship. However, it is difficult for freehand preparation to get a favorable proximal contour in some cases. In the workflow presented here, virtual grinding can be made to adjacent teeth, under the consideration of functional reconstruction and biological requirements, and then the grinding can be implemented using digital templates and a specialized bur. This allows for more precise and accurate adjustments to be made during the clinical procedure, reducing the risk of over- or under-preparation of the proximal surfaces. In addition, the use of specialized diamond burs and grinding guides can make the procedure more efficient and streamlined, reducing the time required for proximal adjustment and minimizing patient discomfort. The resulting implant-supported prosthesis is more likely to function properly and last longer, as the precise proximal contacts can help distribute occlusal forces more evenly across the dentition. Overall, the use of digital technology for precise adjustment of proximal contacts during implant restorations represents an important advancement in modern dentistry, enabling dentists to provide their patients with more accurate, efficient, and effective dental care.

Prevalence of different types of interproximal contacts in the permanent dentition - a study cast evaluation

Background

A new classification called OXIS was proposed for categorizing the interproximal contacts of primary molars, modified for the primary canines and its prevalence was established. No such information is available for the permanent dentition. Hence, the aim was to establish the variations in interproximal contacts of the permanent dentition and thereby modify the OXIS classification of primary molars and primary canines to the permanent dentition.

Methods

We propose a study-cast-based classification of interproximal contacts of the permanent dentition. Three hundred and forty-three pretreatment casts of patients based on an inclusion and exclusion criteria were selected. Contacts of posterior teeth were classified based on OXIS classification of interproximal contacts, and its modification was used for anterior teeth.

Results

Among the posterior contacts, the 'O' type of contact was least prevalent, while most prevalent was the 'S' type for second molar-first molar contact, 'I' type for the first molar-second premolar contact, and 'X' type for the second premolar-first premolar contact. Among the anterior contacts, least prevalent was 'S1' type for the first premolar-canine contact, and I type for the canine-lateral incisor and the lateral incisor-central incisor contacts. There was no statistical significance between right- and left-side contacts ( P > 0.05) while significance was seen between maxillary and mandibular contacts ( P < 0.05). Similarity of contacts ranged from 5.17% to 10.05%.

Conclusion

The OXIS classification is applicable to posterior permanent teeth, and its modification is representative of anterior permanent teeth.

Evaluation of enamel thickness of mandibular incisors

OBJECTIVE

To measure enamel thickness at the proximal surfaces of the mandibular incisors, using micro-computed tomography (micro-CT) scans.

MATERIAL AND METHODS

Forty-one single-rooted mandibular incisors were selected and analyzed according to anatomical characteristics, to form three groups: Group 1 - central incisors (n = 18); Group 2 - right lateral incisors (n = 10); and Group 3 - left lateral incisors (n = 13). First, enamel thickness at the proximal contact areas of the mandibular incisors was measured. Second, the mesial and distal surfaces of the lateral incisors were compared. Finally, the relationship between the tooth width and the mean enamel thickness was determined. Each tooth was scanned with a micro-CT scanner, and the image was processed with SCANCO micro-CT onboard analysis software.

RESULTS

There were no statistically significant differences in mean enamel thickness between the mesial and distal surfaces for each lateral incisor, or between contralateral lateral incisors. In all surfaces analyzed, the upper zones had statistically significantly thinner enamel (0.52 ± 0.10 mm) when compared to the middle and lower zones (0.60 ± 0.08 mm and 0.59 ± 0.08 mm, respectively). There was no correlation (r =0.07) between enamel thickness of the mandibular incisor and the tooth width.

CONCLUSIONS

The enamel thickness of the mandibular incisors is similar on the mesial and distal surfaces, with the thinnest layer located at the upper zone.

Finite Element Analysis of Orthodontic Relapse in Different Maxillary Arch Form

Abstract Background: Orthodontic relapse is fairly common; however, the mechanisms between relapse and the dental arch form remain unclear. The purpose of our study was to establish three-dimensional (3D) finite element models of different dental arch forms after orthodontic treatment and to analyze the states of different arches applied with various sagittal forces.Methods: By calculating the equations of different dental arch forms and combining them with a full maxillary arch (14 teeth), 3D finite element models of square, oval, and tapered dental arches were established; they were designed to be subjected to anterior lingual, posterior mesial, and combined forces, respectively.Results: The von Mises stress and displacement of teeth under different forces were calculated for each loading scenario. Under the different forcing scenarios, all incisors had irregularity trends, and the inclination and intrusion of the canines were increased, and the premolars had a tendency to buccal or lingual crown tipping or even intrusion in our study. The tapered arch was the most stable and had the smallest displacement and von Mises stress, followed by the ovoid arch; the most unstable arch was the square arch.Conclusions: To achieve a stable orthodontic effect, a tapered or ovoid arch, rather than a square arch, should be chosen as the final outcome of treatment.

Proximal enamel thickness of the permanent teeth: A systematic review and meta-analysis

INTRODUCTION

This systematic review aimed to identify, evaluate, and provide a synthesis of the available literature on the proximal enamel thickness (PET) of permanent teeth.

METHODS

The eligibility criteria were studies that assessed the PET of the permanent teeth. A search of studies in Medline (via PubMed), the Cochrane Library, Scopus, Web of Science, Embase, and Lilacs databases that measured PET was conducted until August 31, 2020. Two reviewers independently selected the studies, extracted the data, and assessed the risk of bias for systematic reviews involving cross-sectional studies. The quality of evidence was assessed using the Grading of Recommendations, Assessment, Development, and Evaluations approach. PET data generated from the systematic review were summarized by random-effects inverse-generic meta-analysis.

RESULTS

From 1388 potentially eligible studies, 11 were considered for systematic review and meta-analysis. The measurement of PET was done with radiographs, microscopes, microtomographs, or profilometers. In total, 4019 mesial and distal surfaces involving 2118 teeth were assessed. All included studies showed low to moderate risk of bias, whereas GRADE revealed that the level of evidence was low. Greater mesial and distal enamel thickness was observed for the premolars and molars, whereas it was least for the mandibular central incisors. The least difference of 0.02 mm (95% confidence interval [CI], -0.07 to 0.11 and -0.06 to 0.09, respectively) between mesial and distal sides was observed for the maxillary and mandibular second molars, whereas the maximum difference of 0.12 mm (95% CI, 0.07-0.17 and 0.07-0.16, respectively) was observed for the maxillary central incisors and maxillary first premolars. The meta-analysis indicated a moderate level of heterogeneity (I² of 45%). The funnel plot revealed minimal publication bias.

CONCLUSIONS

The summary effect of the meta-analysis revealed that the thickness of the enamel on the distal aspect was greater than on the mesial aspect by an average of 0.10 mm (95% CI, 0.09-0.12). This finding would be of relevance to all disciplines of dentistry and especially for the clinician planning interproximal reduction, a procedure that is routinely done for clear aligner therapy.

Quantitative evaluation of implemented interproximal enamel reduction during aligner therapy

OBJECTIVES

To investigate the correspondence between programmed interproximal reduction (p-IPR) and implemented interproximal reduction (i-IPR) in an everyday-practice scenario. The secondary objective was to estimate factors that might influence i-IPR to make the process more efficient.

MATERIALS AND METHODS

Fifty patients treated with aligner therapy by six orthodontists were included in this prospective observational study. Impressions were taken at the beginning of treatment and after the first set of aligners. Data on p-IPR, i-IPR and technical aspects of IPR were gathered for 464 teeth. Statistical analyses included the Wilcoxon signed-rank test, Kruskal-Wallis, and multilevel mixed regression.

RESULTS

Mean difference between p-IPR and i-IPR was 0.15 mm (SD: 0.14 mm; P = .0001), with lower canines showing the highest discrepancy. Use of burs and measuring gauges resulted in a smaller difference (respectively: coeff.: 0.09, P = .029; coeff.: -0.06, P = .013). IPR was performed more accurately on the mesial surface of teeth than on the distal surface. Round tripping before IPR resulted in a slightly more precise i-IPR compared to the previous alignment (coeff.: -0.021, P = .041).

CONCLUSIONS

Implemented IPR tends to be less than p-IPR, especially for lower canines and distal surfaces of teeth. Burs tend to provide more precise i-IPR, especially compared to manual strips; however, there is variation between the techniques. Using a measuring gauge tends to increase the precision of i-iPR. As several factors influence the implementation of IPR, particular attention must be paid during the procedure to maximize its precision.

Enamel thickness of maxillary canines evaluated with microcomputed tomography scans

INTRODUCTION

Enameloplasty of maxillary canines is often needed for aesthetic substitution in patients with congenitally missing lateral incisors. The exact enamel thicknesses for the various canine surfaces are unknown because previous studies failed to employ accurate measurement tools to report and compare detailed enamel thicknesses for each surface at various crown heights.

METHODS

Thirty-two extracted maxillary canines were collected and scanned in a microcomputed tomography scanner. The scans were imported into a custom-written MATLAB software (version 9.2; MathWorks, Natick, Mass) and the enamel thickness on the mesial, distal, labial, fossa, cingulum, and incisal edge of each tooth was computed, obtaining the mean value from slices at 0.1 mm intervals. The overall mean enamel thickness for each surface was also calculated, and these values were compared using paired t tests. Incisal wear stage and incisal enamel thickness that was measured were compared using Spearman rank correlation coefficient.

RESULTS

The mean enamel thickness was significantly thinner at the gingival level when compared with the incisal for all surfaces that were analyzed (1-tailed, P <0.001). The mean enamel coverage at the mesial was significantly thinner than the distal when measured gingival to the widest mesiodistal area. The mean enamel coverage of the cingulum was particularly thin and therefore requires extreme care in reshaping it. Incisal edge enamel thickness was highly negatively correlated with the wear stage of the scoring system that was used (1-tailed, P <0.001).

CONCLUSIONS

The enamel coverage of the maxillary canine varies depending on the tooth surface and the incisogingival measurement location.

Depth of acid penetration and enamel surface roughness associated with different methods of interproximal enamel reduction

Objectives

To assess and compare the enamel surface quality after interproximal enamel reduction (IPR) was performed with different systems and to study the relation between acid penetration depth and enamel surface quality as well as the importance of remineralization.

Methods

Sixty-five extracted teeth were randomly allocated to five experimental groups: untreated control, manual with New Metal Strips, mechanical with oscillating segment (OS) discs, Safe-Tipped Bur Kit, and the Ortho-Strip, followed by 30 s of polishing with the Softflex system and the Compo-system after treating the tooth with OS discs. Mesial surfaces were demineralized for 24 h and distal surfaces were subjected to interchanging demineralization and remineralization cycles of 24 h each for 18 days. The analysis was carried out by profilometry, scanning electron microscopy, and polarization microscopy.

Results

After IPR and polishing, enamel roughness was reduced for all systems tested except for the Essix Safe-Tipped Bur Kit. Subsequent demineralization increased enamel roughness in all groups except controls beyond the original level prior to IPR except for IPR with New Metal Strips or Ortho-Strips and subsequent polishing. Cyclic demineralization and remineralization for 18 days yielded a reduction in acid penetration depth and an increase in surface smoothness, which correlated with each other only for controls and treatment with New Metal Strips or Ortho-Strips.

Conclusions

Manual IPR, using New Metal Strips and, even more, the oscillating IPR system Ortho-Strips, yielded smoother interproximal enamel surfaces and less acid penetration depth than the IPR systems with OS discs and the Safe-Tipped Bur Kit after polishing and 18 days of cyclic demineralization and remineralization. Irrespective of the IPR procedure, proper remineralization of IPR-treated surfaces is advisable to reduce caries susceptibility.

Posterior Available Space for Uprighting Horizontally Impacted Mandibular Second Molars Using Orthodontic Microimplant Anchorage

Treatment of horizontally and deeply impacted mandibular molars is challenging for both orthodontists and oral surgeons because of the limited access and anchorage control. We report on two patients who had horizontally and mesially impacted mandibular second molars (MM2s). Both patients were treated by a surgical orthodontic approach, and the crowns of the impacted teeth were brought into the arches by closed forced eruption. Mesially impacted MM2s were uprighted with orthodontic microimplants, inserted in the retromolar area, and then moved into their ideal position. The first patient was in an active growing stage, while the second patient was beyond the active growing stage. Therefore posterior available space (PAS) should be analyzed before treatment of impacted MM2s to prevent periodontal problems after uprighting of impacted teeth. If PAS is not enough for uprighting impacted MM2s, alternative treatment should be considered based on the stage of growth.

Total arch distalization with interproximal stripping in a patient with severe crowding

When a patient shows severe crowding, premolar extraction should be considered to provide required available space for alignment. If the third molars have already erupted and demonstrate a poor prognosis, third molar extraction and distalization of the posterior dentition can be used instead of premolar extraction to obtain space. Interproximal stripping (IPS) may also be used to gain space in cases of crowding. This case report describes the treatment of a 25-year-old man with severe crowding and mild lip protrusion. Although the crowding in the lower arch was severe enough to require first premolar extraction, distalization of the entire lower dentition with orthodontic mini-implants, extraction of the lower third molars, and IPS could successfully resolve the crowding and lip protrusion.

Proposed classification for interproximal contacts of primary molars using CBCT: a pilot study

Background: Interproximal contact areas in primary teeth are known to be broader, flatter, and situated more gingivally than in permanent teeth. The objective of the present study was to evaluate the different types of intact interproximal contact areas in primary teeth using cone beam computed tomography (CBCT) among children. Methods: A cross-sectional study was designed with 74 contacts from 28 existing CBCT images of children aged between 3 and 14 years, obtained from the Indian Dental Education Academy, Chennai, India. The shape of the contact area was observed at three levels, the coronal, middle, and apical thirds, in three different sections of CBCT. Prevalence of the types of contact areas was expressed in the form of numbers and percentages. Results: The weighted Cohen's kappa values for inter-examiner reliability was 0.893 at baseline. Results exhibited four different types of contact areas between the primary molars, namely, O type, X type, I type, and S type, based on the shapes observed; hence, the proposed classification is referred to as OXIS. The most common pattern seen was I (66.2%), followed by X (21.6%), O (9.4%) and the least common was S (2.7%). Conclusion: The three-dimensional evaluation of intact interproximal contact areas between primary molars are of four types, O,X, I and S.

Proposed classification for interproximal contacts of primary molars using CBCT: a pilot study

Background: Contact areas in primary teeth are known to be broader, flatter, and situated more gingivally than in permanent teeth. The objective of the present study was to evaluate the different types of intact contact areas in primary teeth using cone beam computed tomography (CBCT) among children. Methods: A cross-sectional study was designed with 74 contacts from 28 existing CBCT images of patients aged between 3 and 14 years, obtained from the Indian Dental Education Academy, Chennai, India. The shape of the contact area was observed at three levels, the coronal, middle, and apical thirds, in three different sections of CBCT. The weighted Cohen's kappa values for inter-examiner reliability was 0.893 at baseline. Prevalence of the types of contact areas was expressed in the form of numbers and percentages. Results: Results exhibited four different types of contact areas between the primary molars, namely, O type, X type, I type, and S type, based on the shapes observed; hence, the proposed classification is referred to as OXIS. The most common pattern seen was I (66.2%), followed by X (21.6%), O (9.4%) and the least common was S (2.7%). Conclusion: The three-dimensional evaluation of intact interproximal contact areas between primary molars are of four types.

In vitro study of white spot lesion: Maxilla and mandibular teeth

Aim

The aim of the study was to evaluate the effect of resin infiltration on colour changes and surface roughness of artificial white spot lesions (WSLs) on maxillary and mandibular premolar.

Materials and methods

Sixty (60) extracted sound Maxilla (Mx) and Mandibular (Mn) premolars were randomly divided into 2 groups (test and control). Artificial WSLs were produced on buccal surface of teeth and were immersed in artificial saliva for 8 weeks. Colour components (L^∗, a^∗, b^∗) and surface roughness (Sa^∗) were assessed on 40 teeth using colour difference meter RD-100 and Alicona® Infinite Focus profilometer respectively. The measurements were done at baseline (T1), directly after artificial WSLs (T2), after 24 hours immersed in saliva and application of resin (T3) and immersion in artificial saliva for 1 (T4), 2 (T5), 4 (T6), 6 (T7) and 8 (T8) weeks. SEM images analysis were carried out on 20 teeth in four time points.

Results

The values of L^∗ (lightness), b^∗ (yellow/blue) and Sa^∗ (surface roughness) are gradually reduced to the baseline value. Whereas, the value of a^∗ gradually increased with distinct treatment time to achieve the baseline value. The higher value of L^∗ and Sa^∗, the whiter the lesion suggesting higher degree of enamel demineralization and surface roughness. Lower L^∗ values suggest a masking colour effect.

Conclusion

The material produced favorable esthetics on colour and the surface roughness of teeth at distinct treatment times. It is recommended to be used to improve WSL post orthodontic treatment.

Radiographic technique and brackets affect measurements of proximal enamel thickness on mandibular incisors

OBJECTIVE

To investigate the influence of radiographic film and tube positioning, the presence and the size of brackets on in vitro measurements of proximal enamel thickness of mandibular incisors on periapical radiographs aimed to aid planning of interproximal enamel reduction procedures in orthodontics.

MATERIALS AND METHODS

Eighty human mandibular incisors were assigned to sets of four and located in a customized base. Periapical radiographs were taken with the film positioned at three different angles (0°, 2°, and 5°) in relation to the frontal plane and the tube head positioned at five angles (0°, -2°, -5°, +2°, and +5°) in relation to the sagittal plane. The proximal enamel width was calculated by means of computerized image analysis and compared with measurements obtained at 0°. Statistical analysis was carried out to compare the enamel measurements on radiographs made with all angular combinations with and without the presence of brackets of different dimensions.

RESULTS

A significant difference (P < 0.05) was found between the measurements of proximal enamel width obtained at the different angles in relation to the frontal and sagittal planes for all sets with or without brackets. The presence of brackets significantly affected the measured width only for the enamel side further away from the radiation source at the sagittal plane (P < 0.05).

CONCLUSION

Angular changes in taking periapical radiographs of mandibular incisors and the presence of brackets significantly affect interproximal enamel measurements made with image analysis software.

Quantitative sensory testing of dentinal sensitivity in healthy humans

OBJECTIVE

The study was to provide information on quantitative sensory testing (QST) of normal teeth to establish a sensory profile and investigate the possible gender and regional differences.

MATERIALS AND METHODS

A modified QST protocol was applied on both left and right upper-jaw incisors and pre-molar sof 14 healthy men and 14 age-matched healthy women (18-25 years). Mechanical stimulus sensitivity (MSS), cold detection threshold (CDT), cold pain threshold (CPT), warm detection threshold (WDT), heat pain threshold (HPT), electrical detection threshold (EDT) and electrical pain threshold (EPT) were determined from the four teeth (labial side of incisor and buccal side of the first premolar). The QST parameters were analysed by ANOVA.

RESULTS

The applied mechanical or thermal stimuli did not evoke any pain sensation. A normal tooth did not seem to be able to distinguish between the warm or cold stimuli applied. No significant differences were found between genders (p > 0.099) or teeth (p > 0.053) regarding mechanical and thermal stimuli. The EDT and EPT were significantly higher in the pre-molar compared with incisor (p < 0.002) without gender differences (p > 0.573).

CONCLUSION

The established methods and results provided important information on diagnosis and treatment evaluation of dentinal hypersensitivity.