Rehabilitation of occlusion - science or art?

A digital, custom gothic arch tracing technique for vertical dimension of occlusion and centric relation recording

A method for identifying the vertical dimension of occlusion and centric relation in patients requiring dental rehabilitation is described. The technique relies on designing and fabricating a custom variant of the gothic arch tracer based on intraoral scans and its application following the principles of neuromuscular balance of the stomatognathic system.

An evaluation of dental practitioner habits with occlusal assessment and the clinical application of practical techniques in occlusion, amongst a cohort of participants based in the UK , South Africa, Malta, and Malaysia

Background

Objectives

Methods

Results

Conclusion

Hypothetical Model of How a Clinical Remount Procedure Benefits Patients with Existing Dentures: A Narrative Literature Review

The clinical remount procedure, which involves remounting the dentures on an articulator with interocclusal records, can effectively reduce occlusal discrepancies. This procedure can be applied not only to new dentures but also to those already in service; however, research in this field is still scarce. This narrative review aims to establish a hypothetical mechanism and possible indications and contraindications for this technique as a basis for further research. Current studies have revealed a high prevalence of malocclusion in delivered dentures. Performing a clinical remount on these existing dentures would enhance the oral function of the denture wearer and would enable effective and accurate correction of the accumulated errors in the jaw relationship in a stable working environment. This technique should be performed if a patient has poor masticatory function or occlusion-related complaints. However, performing a clinical remount on dentures with an excessive anterior–posterior discrepancy between the centric relation and the maximal intercuspal position or on dentures with extremely low occlusal vertical dimension, is considered less effective. The clinical remount procedure remains an essential skill both for fabricating quality dentures and maintaining those already in service.

Can Botulinum Toxin-A Contribute to Reconstructing the Physiological Homeostasis of the Masticatory Complex in Short-Faced Patients during Occlusal Therapy? A Prospective Pilot Study

The physiological homeostasis of the masticatory complex in short-faced patients is too robust to be disintegrated and reconstructed due to the powerful masseter muscle. This study innovatively introduced the botulinum toxin-A (BTX-A) into the field of dental occlusal treatment, providing a novel and minimally invasive therapy perspective for the two major clinical problems in these patients (low treatment efficiency and high rates of complications). In total, 10 adult patients with skeletal low angle seeking occlusal treatment (age: 27.0 ± 6.1 years; 4 males and 6 females) were administered 30−50 U of BTX-A in each masseter muscle and evaluated before and 3 months after injection based on cone-beam computed tomography (CBCT). We found a significant reduction in the thickness of the masseter muscle (MMT) (p < 0.0001). With regards to occlusion, we found a significant increase in the height of the maxillary second molar (U7-PP) (p < 0.05) with significantly flattened occlusal curves (the curve of Spee [COS] (p < 0.01), and the curve of Wilson [COW] (p < 0.05)). Furthermore, the variations in the temporomandibular joint exhibited a significant reduction in the anterior joint space (AJS) (p < 0.05) and superior joint space (SJS) (p < 0.05). In addition, the correlation analysis of the masticatory complex provided the basis for the following multiple regression equation: MMT = 10.08 − 0.11 COW + 2.73 AJS. The findings from our pilot study indicate that BTX-A, as a new adjuvant treatment attempt of occlusal therapy for short-faced patients, can provide a more favorable muscular environment for subsequent occlusal therapy through the adjustment of the biting force and may contribute to the reconstruction of healthier homeostasis of the masticatory complex. However, further research is required to establish the reliability and validity of these findings.

Oral Function Rehabilitation with the Simplified Lauritzen Clinical Remount Technique in a Patient with Bimaxillary Alveolar Exostoses: A Case Report

This case report describes a 70 year-old man with IVA lung cancer who required oral function rehabilitation by fabricating dentures with a simplified clinical remount technique. A pair of dentures were fabricated for a 70-year-old man with stage IVA lung cancer. Due to severe bimaxillary exostoses, the dentures could not properly extend and achieve a peripheral seal. The treatment philosophy was to stabilize the dentures and achieve proper function with optimized occlusion. The simplified Lauritzen clinical remount technique was performed at the time of denture delivery and 3 months later. After the second clinical remount procedure, the patient was able to eat meals with the dentures and maintained in a stable condition. Compared with the original technique, the simplified Lauritzen clinical remount omits the facebow transfer and keeps the condylar guidance setting and the Bennett angle unchanged during the adjustment. The prostheses are mounted to a type 3, non-arcon type articulator with anterior stop screws attached to the bilateral condylar parts. With the aid of anterior stop screws, the eccentric movement of dentures can be differentiated on a millimeter scale and balanced easily. It is effective to use occlusal-optimized dentures and the clinical remount technique, especially in difficult cases.

Reliability and validity of a new colour-changing test food with an acid-base reaction for the clinical assessment of masticatory performance

The aim of this study was to determine the reliability and validity of a new test food for the clinical assessment of masticatory performance. The test food had two overlapping acidic/basic halves. Ten dentate subjects chewed one unit for 10-100 cycles. One subject chewed ten units for the same number of cycles. Differences in the L*, a* and b* colour axes were determined before and after chewing by ANOVA. Colour guides were created based on the values of these axes and matched with the number of cycles. The reliability of the guides was evaluated using 30 images, where three examiners indicated the number of cycles in which the colour closest to that of a chewed material was found. The data were contrasted with the real values of the guides to determine the validity (Kappa coefficients). The equivalence of the guides with the median particle size (X₅₀) was determined using equidimensional curves. The test food progressively changed from green to pink during chewing. As the number of cycles increased, the a* values increased and the b* values decreased (p < 0.05). Overall, the guides showed a Kappa value >0.8 for the intra-examiner and inter-examiner reliability and the validity comparisons. The a* and X₅₀ values were inversely proportional to each other, and the b* values showed a direct relationship with the X₅₀ values. The L* values did not show correspondence. The new test food showed high reliability and validity for the assessment of masticatory performance through clinical colour guides matched with the number of cycles and X₅₀.

Comparison of two arbitrary cast transfer systems with a kinematic facebow for mounting a maxillary cast on a semiadjustable articulator

STATEMENT OF PROBLEM

The Kois Dento-Facial Analyzer (KDFA) is used by clinicians to mount maxillary casts and to evaluate and treat patients. Limited information is available for understanding whether the KDFA should be considered as an alternative to an arbitrary facebow.

PURPOSE

The purpose of this clinical study was to evaluate and compare maxillary casts mounted by using the KDFA with casts mounted by using the Panadent Pana-Mount Facebow (PMF) and a kinematic axis (KA) facebow.

MATERIAL AND METHODS

Fifteen participants were enrolled in the study. Three maxillary impressions were made of each study participant. One cast from each study participant was mounted on an articulator by means of the KDFA, PMF, and KA. A standardized photograph of each mounting was made, and the condylar center-incisor distance and the occlusal and incisal plane angles were measured. A randomized complete block design analysis of variance (RCBD) (α=.05) and post hoc tests (Tukey-Kramer HSD) were used to evaluate the occlusal and incisal plane angles and the condylar center-incisor distance.

RESULTS

Compared with the occlusal plane angle (OPA), the KDFA mounted the maxillary cast at an angle that was statistically lower than those of PMF and KA (P<.001). The KDFA and the PMF condylar center-incisor distances were both significantly greater than that of KA (P=.01). No differences were found between the incisal plane angle (IPA) on maxillary casts mounted with the KDFA, KA, or PMF (P=.16).

CONCLUSIONS

The KDFA and PMF mounted the maxillary casts in a position that was farther from the axis when compared with the KA mounted casts. The KDFA resulted in a lower articulator OPA compared with both PMF and KA. No difference was found between the IPAs of the KDFA, PMF, and KA.

Occlusal Concepts and Considerations in Fixed Prosthodontics

The UK has an increasingly ageing population, many of whom are retaining more of their own teeth. This has led to an increase in the prevalence of tooth wear and the need to replace pre-existing failing restorations. In many cases this will be achieved by fixed prosthodontics. This paper provides a brief overview of important occlusal concepts that should be considered when providing non-implant fixed prosthodontics using either a conformative or reorganised approach. The aim is to give general dental practitioners the confidence to provide these types of restorations in primary care. Clinical cases demonstrate how the occlusion can be controlled to optimise clinical outcomes.

Comparison reproducibility between the facebow and a new technique based on a spirit level device

Objective: This study aimed to introduce a spirit level device for mounting maxillary casts to compare the reproducibility between the facebow and this new technique.Methods: The maxillary casts of 10 participants were mounted in three different situations: 1) with the facebow; 2) with the spirit level device, the participant in seated position; and 3) with the spirit level device with participant in standing position. Each procedure was performed by three different evaluators. The values obtained were calculated using the Technical Error of Measurement (TEM) and the inter-evaluator Coefficient of Variation (CV).Results: The mean values obtained were 4.3 mm, 2.2 mm, and 2.6 mm for absolute TEM; 8.7%, 5.4%, and 6.4% for relative TEM; and 7.3%, 4.5%, and 5.6% for CV.Conclusion: These results show that the facebow is less reproducible compared to the new device, demonstrating that the new technique can be satisfactorily used in clinical practice.

The restorative management of tooth wear involving the aesthetic zone

The aim of this article is to describe a systematic approach that facilitates the establishment of a clear and appropriate diagnosis when a dentate patient presents with tooth wear involving their aesthetic zone. It will also detail the protocols that are required to allow for the development of an acceptable aesthetic prescription within the limits of the functional constraints presented by the patient (where active restorative intervention may be indicated), as well as to communicate the manner by which this information can be transferred to ultimately enable the successful and predictable rehabilitation of the affected areas. An overview will also be provided of the tooth-coloured dental materials and restorative techniques that have been commonly applied to deliver the predictable and effective dental care of worn teeth in the aesthetic zone.

Extraction of maxillary canines: Esthetic perceptions of patient smiles among dental professionals and laypeople

INTRODUCTION

Maxillary canines are generally considered important both cosmetically and functionally. Most claims on the importance of maxillary canines, however, have been based on expert opinions and clinician-based studies. There are no scientific studies in the literature reporting on their cosmetic importance or how laypeople perceive a smile treated by maxillary canine extractions. Our objective was to investigate whether there is any difference in the perceptions of patients' smiles treated by extracting either maxillary canines or first premolars, as judged by orthodontists, dentists, and laypeople.

METHODS

This retrospective study included 24 participants who had unilateral or bilateral extraction of maxillary permanent canines and fixed appliances in the maxillary and mandibular arches to comprehensively correct the malocclusion, selected from orthodontic patients treated at Chesterfield Royal Hospital NHS trust in the United Kingdom over the last 20 years. The control group of patients had extraction of maxillary first premolars followed by fixed appliances and finished to an extremely high standard judged by the requirement that they had been submitted for the Membership in Orthodontics examination. The finished Peer Assessment Rating scores for this group were less than 5. The end-of-treatment frontal extraoral smiling and frontal intraoral views were presented for both groups. The photographs were blinded for extraction choice and standardized for size and brightness using computer software (Adobe Photoshop CC version 14.0; Adobe Systems, San Jose, Calif). The work file was converted to an editable pdf file and e-mailed to the assessors. The assessor panel consisted of 30 members (10 orthodontists, 10 dentists, and 10 laypeople), who were purposely selected. The measures were rated on a 10-point Likert scale.

RESULTS

The attractiveness ratings were not statistically significantly different between the canine extraction and premolar extraction groups, with a mean difference of 0.33 (SD, 0.29) points. A 1-way repeated-measures analysis of variance to test the difference in scores among the laypeople, orthodontists, and dentists (n = 30) showed no statistically significant difference (Wilks lambda = 0.835; P = 0.138), and the Bonferroni test indicated that no pair-wise difference was statistically significant.

CONCLUSIONS

No statistically significant difference was found in the smile attractiveness between canine extraction and premolar extraction patients as assessed by general dentists, laypeople, and orthodontists. Further high-quality studies are required to evaluate the effect of canine extraction and premolar substitution on functional occlusion.

Evaluation of functional parameters in the occlusion of complete denture wearers before and after prosthetic treatment

PURPOSE

The aim of the study was to evaluate functional parameters of the occlusion in complete denture wearers before and after prosthetic treatment.

METHODS

The sample used as the basis for the present study consisted of 50 healthy Caucasian patients (35 women and 15 men), aged from 44 to 86 years (mean=69.18±10), with a total deficiency of teeth. All patients received new complete dentures. Each patient underwent lateral radiograph with the presence of complete dentures, both before (initially existing dentures) and after the prosthetic treatment (new restorations). Cephalometric analysis was based on the Ricketts and McNamara criteria. In order to assess the functional parameters of the occlusion T-scan III analysis was conducted. The following parameters were measured: occlusion - and disclusion time.

RESULTS

Statistically significant differences of functional parameters obtained before and 3 months after the treatment were noted in the whole study group. Both before and after therapy occlusion time was longer in women than in men. No statistically significant link was noted between functional parameters in occlusion and age of the patients, denture wearing time, and edentulous period. Some relationships were noted between occlusion time and cephalometric parameters associated with anterior facial height.

CONCLUSION

Reconstruction of the surface of artificial teeth and vertical occlusal dimension affects the sustainability of parameters of occlusion and balance of forces in centric occlusion. The progressive shortening of occlusion time during the period of monitoring may be considered as a sign of progressive adaptation.

Occlusal consequence of using average condylar guidance settings: An in vitro study

STATEMENT OF PROBLEM

A simplified mounting technique that adopts an average condylar guidance has been advocated. Despite this, the experimental explanation of how average settings differ from individual condylar guidance remains unclear.

PURPOSE

The purpose of this in vitro study was to examine potential occlusal error by using average condylar guidance settings during nonworking side movement of the articulator.

MATERIAL AND METHODS

Three-dimensional positions of the nonworking side maxillary first molar at various condylar and incisal settings were traced using a laser displacement sensor attached to the motorized stages with biaxial freedom of movement. To examine clinically relevant occlusal consequences of condylar guidance setting errors, the vertical occlusal error was defined as the vertical-axis positional difference between the average setting trace and the other condylar guidance setting trace. In addition, the respective contribution of the condylar and incisal guidance to the position of the maxillary first molar area was analyzed by multiple regression analysis using the resultant coordinate data.

RESULTS

Alteration from individual to average settings led to a positional difference in the maxillary first molar nonworking side movement. When the individual setting was lower than average, vertical occlusal error occurred, which might cause occlusal interference. The vertical occlusal error ranged from -2964 to 1711 μm. In addition, the occlusal effect of incisal guidance was measured as a partial regression coefficient of 0.882, which exceeded the effect of condylar guidance, 0.431.

CONCLUSIONS

Potential occlusal error as a result of adopting an average condylar guidance setting was observed. The occlusal effect of incisal guidance doubled the effect of condylar guidance.

Consequences of experience and specialist training on the fabrication of implant-supported prostheses: A survey

STATEMENT OF PROBLEM

Fabricating fixed restorations on implants requires that dentists stay up-to-date with the scientific publications.

MATERIAL AND METHODS

A questionnaire containing 29 questions was sent to dentists, members of the Israeli Society of Prosthodontics, and university faculty members. Differences were evaluated using the chi-square and Fisher exact tests and Mann-Whitney U and Wilcoxon tests for questions enquiring into the frequency of use of certain methods (α=.05).

RESULTS

A total of 155 questionnaires were completed by 84 general dental practitioners and 71 specialists and residents. Statistical differences (P<.05) were found in the course of the fabrication of the implant-supported prostheses in the diagnostic waxing, trial restoration, and impression-making processes. Trial restorations were often used by residents and specialists before starting an esthetic restoration. Diagnostic waxing was used when treating patients with complex esthetic needs, mainly by prosthodontists (P=.019). A custom tray for impression making was used more by residents and specialists than by general dental practitioners (P<.001). The open tray technique for impression making of single or up to 3 implants was performed mainly by residents, specialists, and general dental practitioners with professional experience of fewer than 15 years. General dental practitioners used primarily plastic or metal trays for impression making.

CONCLUSIONS

Significantly, impression techniques and the use of custom open trays, diagnostic waxing, and trial restorations were performed by residents, specialists, and dentists with fewer than 15 years of experience.

Effect of prosthodontic planning on intercuspal occlusal contacts: comparison of digital and conventional planning

BACKGROUND

Adequate occlusal contacts are critical for masticatory function. The aim of this study is to evaluate the intercuspal occlusal contacts following conventional and digital wax-ups.

METHODS

Stone casts of 15 patients undergoing prosthodontic treatment were gathered. Each cast was duplicated twice, so that conventional and digital wax-ups could be performed. To assess the occlusion, the following variables were evaluated: contact number per tooth (CNT), contact area per tooth (CAT) and contact accuracy. Further, the impact of tooth location in the arch was assessed.

RESULTS

The CNT and CAT after the wax-ups increased significantly following each wax-up, and this increase was more prominent for the posterior teeth than the anterior teeth. The conventional wax-up was associated with lower CNT than the digital wax-up, especially for the posterior teeth. On the other hand, the CAT was greater for the conventional wax-up than the digital wax-up for the anterior and posterior teeth. In terms of accuracy, the two wax-ups showed greater discrepancies than the pre-treatment casts, however, the magnitude of discrepancy was greater for the digital wax-up.

CONCLUSIONS

The two wax-ups improved the contact number and area. Despite the statistical variation between the wax-ups, the actual difference was minimal. Therefore, it could be speculated that the two wax-ups produced a similar outcome.

Biomechanical factors related to occlusal load transfer in removable complete dentures

Owing to economic conditions, removable dentures remain popular despite the discomfort and reduced chewing efficiency experienced by most denture wearers. However, there is little evidence to confirm that the level of mucosal load exceeds the pressure pain threshold. This discrepancy stimulated us to review the current state of knowledge on the biomechanics of mastication with complete removable dentures. The loading beneath dentures was analyzed in the context of denture foundation characteristics, salivary lubrication, occlusal forces, and the biomechanics of mastication. The analysis revealed that the interpretation of data collected in vivo is hindered due to the simultaneous overlapping effects of many variables. In turn, problems with determining the pressure beneath a denture and analyzing frictional processes constitute principal limitations of in vitro model studies. Predefined conditions of finite element method simulations should include the effects of oblique mastication forces, simultaneous detachment and sliding of the denture on its foundation, and the stabilizing role of balancing contacts. This review establishes that previous investigations may have failed because of their unsubstantiated assumption that, in a well-working balanced occlusion, force is only exerted perpendicular to the occlusal plane, allowing the denture to sit firmly on its foundation. Recent improvements in the simulation of realistic biomechanical denture behavior raise the possibility of assessing the effects of denture design on the pressures and slides beneath the denture.

Occlusion on oral implants: current clinical guidelines

Proper implant occlusion is essential for adequate oral function and the prevention of adverse consequences, such as implant overloading. Dental implants are thought to be more prone to occlusal overloading than natural teeth because of the loss of the periodontal ligament, which provides shock absorption and periodontal mechanoreceptors, which provide tactile sensitivity and proprioceptive motion feedback. Although many guidelines and theories on implant occlusion have been proposed, few have provided strong supportive evidence. Thus, we performed a narrative literature review to ascertain the influence of implant occlusion on the occurrence of complications of implant treatment and discuss the clinical considerations focused on the overloading factors at present. The search terms were 'dental implant', 'dental implantation', 'dental occlusion' and 'dental prosthesis'. The inclusion criteria were literature published in English up to September 2013. Randomised controlled trials (RCTs), prospective cohort studies and case-control studies with at least 20 cases and 12 months follow-up interval were included. Based on the selected literature, this review explores factors related to the implant prosthesis (cantilever, crown/implant ratio, premature contact, occlusal scheme, implant-abutment connection, splinting implants and tooth-implant connection) and other considerations, such as the number, diameter, length and angulation of implants. Over 700 abstracts were reviewed, from which more than 30 manuscripts were included. We found insufficient evidence to establish firm clinical guidelines for implant occlusion. To discuss the ideal occlusion for implants, further well-designed RCTs are required in the future.