Current status of the neutral zone: A literature review

Complete denture rehabilitation for a patient with Parkinson's disease using clinical strategies: A case report

OBJECTIVE

To present clinical strategies for prosthetic rehabilitation with complete dentures (CDs) of a Parkinson's disease patient.

CASE REPORT

An 82-year-old patient sought the Department of Dentistry at UFRN, reporting retention dissatisfaction and hamper to the mandibular CD adaptation. Patient-reported a dry mouth sensation, and exhibited disordered mandibular movements, tremors, and resorbed mandibular ridge. Aiming retention and stability, double molding with zinc enolic oxide impression paste, neutral zone technique, and non-anatomic teeth were proposed as clinical strategies. At delivery, identification and relief in the supercompression areas were performed to facilitate the acceptance and use of the new dentures.

CONCLUSION

The strategies promoted patient satisfaction regarding retention, stability, and comfort. This treatment may be considered for the rehabilitation of Parkinson's disease patients, favoring the adaptation process.

Influence of edentulism on the structure and function of temporomandibular joint

Background

With the acceleration of the aging process of the population, the number of edentulous patients continuously increased. Edentulism induces the loss of occlusal relationship and cause adverse effects on the stomatognathic system. Temporomandibular joint (TMJ), as a significant component of this system, may also be affected by edentulism in the process of supporting mandibular movement.

Purpose

Provide a comprehensive review of the structure and function of TMJ in the edentulous population, as well as the prevalence of temporomandibular joint disorder (TMD) in edentulous group.

Study selection

An electronic search was conducted on articles prior to December 2022 to filter all papers relevant to the structure and function of TMJ in edentulous population. The internet databases (PubMed, Cochrane Library, Embase) were searched using various combinations of keywords for "edentulism" or "edentulous" and "TMJ" or "TMD".

Results

Firstly, 522 articles were selected from the internet database, and finally, a total of 44 articles met the inclusion and exclusion criteria. The research content of these articles mainly focuses on the structure and function of TMJ in edentulous patients, as well as the clinical signs and symptoms of TMD.

Conclusions

Edentulous arch induces the loss of occlusal relationship, which may lead to degenerative changes of TMJ components consisting of changes in morphology and bone mass density of condyle, articular fossa, and articular eminence. In addition, the condyle could be shifted backward and upward, and displacement of the articular disc may occur after dentition loss. And the condyle and the articular disc may be guided back to the normal position after effective prosthodontic treatment. But the conclusions of the study on the function of TMJ and the prevalence of TMD in edentulous people are inconsistent. The condition of TMJ, especially the position of condyle-fossa and the symptoms and signs of TMD should not be ignored. If necessary, radiographic examinations should be performed.

Integrating a complete denture digital workflow with polished surface registration: A single-procedure clinical protocol

Intraoral digital scanning of edentulous arches has provided the dental profession with the ability to obtain genuinely mucostatic impressions. The drawback, because of the omission of border molding procedures, has been underextended flanges which might affect the retention and stability of the definitive prosthesis. A technique for combining the concept of registering the polished surfaces with a functional impression material and the intraoral digital mucostatic scanning workflow is described.

The Neutral Zone Approach with CAD/CAM Record Bases

Lack of adequate retention, support, and stability in the complete denture can be attributed to a poor fit or incorrect shape of the polished surfaces. This article presents a case using the neutral zone technique effectively with the fabrication of computer-aided design and computer-aided manufacturing (CAD-CAM) record bases in an edentulous patient with severely resorbed alveolar ridges and discusses the overall treatment steps and clinical implications of this technique. A stable neutral zone and an accurate jaw relation were recorded using CAD-CAM record bases and stability of complete denture was optimized by arranging denture teeth and reforming polishing surfaces in the neutral zone. A new complete denture was fabricated for a patient with atrophic alveolar ridges by a technique utilizing the neutral zone with CAD-CAM record bases. This article is protected by copyright. All rights reserved.

Effectiveness of denture space recording method in the prosthetic treatment of edentulous patients

PURPOSE

To present a clinical rationale for the effectiveness of denture space recording methods for the prosthetic treatment of edentulous patients through a review of the literature.

STUDY SELECTION

A total of 3167 studies were extracted from a search of four terms, namely denture space, neutral zone technique, flange technique, and piezography using PubMed and J-STAGE databases. A total of 57 documents that matched the inclusion and exclusion criteria were selected.

RESULTS

From the extracted articles, the clinical application of denture space recording methods was found to be effective in edentulous patients with severe ridge resorption. The relationship between the labiolingual and buccolingual pressure in patients with neuromuscular problems or with mandibular or lingual defects differs from those without it, so a stable prosthesis ca n be easily fabricated by locating the neutral zone using denture space recording methods.

CONCLUSIONS

The literature on denture space recording methods suggests that its application on challenging cases of edentulous patients is useful in providing prostheses with improved retention and stability.

Implant-supported overdentures: part 1

The ability to provide high-quality complete dentures is a key skill for the GDP. The increasing prevalence and utilisation of implant-supported overdentures has opened the possibility of a wide variety of treatment options to support patient care, while also creating the need for primary care practitioners to have a greater awareness of commonly used prosthetic attachments.A thorough understanding of the advantages and disadvantages of implant-supported overdentures is essential to ensuring appropriate treatment planning, consent and maintenance. This two-part series explores various aspects of implant-supported overdentures including assessment of the patient, treatment planning, different attachment systems and maintenance requirements.Part one will explore availability of implants in the NHS, the commonly available implant attachment systems, including their relative advantages and disadvantages.

Ultrashort Implants, Alternative Prosthetic Rehabilitation in Mandibular Atrophies in Fragile Subjects: A Retrospective Study

This study aimed to evaluate the effectiveness of using ultrashort implants in the rehabilitation of jaws of fragile patients. The aim of the study was to retrospectively evaluate the survival rate of full-arch prosthetic rehabilitation on ultrashort implants, length 4 mm, 4 mm in diameter in the premolar and canine area and 4.5 mm in diameter in the molar area, with the insertion torque of 60 Nw and immediate loading. Nineteen patients were evaluated for 3 years clinically and radiographically. The significant majority of the patients at the 3 year follow-up (T4) presented a stable and functional implant-supported prothesis, and the survival rate of the implants was 85%, with a loss of 16 implants on 114 implants. The combination of the innovative implant surfaces and the correct project of the prostheses, with the related implant connection, determined a different timing in the therapy, allowing to obtain an immediate loading, which is currently demanded by patients. This and recent reports on short and ultrashort implant usage in atrophic jaws offer a good solution in critical cases. In conclusion, within the limits of the study, the full-arch rehabilitation with immediate loading on ultrashort implants showed good results with few postoperative complications and related low biological cost.

Neutral zone recording in computer-guided implant prosthesis: A new digital neuromuscular approach

Background

Neutral zone (NZ) is a specific area in the oral cavity where muscular opposite forces are null. NZ represents the ideal zone for prosthesis placement. In this study, we compared digital implant planning using conventional technique and using NZ registration through piezography.

Methods

Sixty-tree implants were digitally planned. Angular deviation differences between traditional planned and NZ-planned implants were calculated. In addition, interferences with soft tissues (i.e., tongue and cheeks) were evaluated.

Results

We observed a significant difference between traditional technique and piezographic approach in terms of implants angulation (p = .003), independent of site. A 4.7% of the planned abutments with traditional technique were placed outside the NZ, causing conflict with soft tissues in the digital model.

Conclusions

Compared with traditional technique, piezography allows a significantly different exploitation of the nonconflict area, which potentially translates into better management of soft tissues and improved functionality of the implants.

Effect on patient satisfaction of mandibular denture tooth arrangement in the neutral zone

STATEMENT OF PROBLEM

The effect of the neutral zone (NZ) technique on different functional aspects (masticatory performance, speech, and muscle activity) has been studied objectively. Subjectively, some studies reported that their participants felt that NZ dentures were more stable, retentive, and comfortable than conventionally fabricated dentures. These studies, however, lacked a measurable assessment scale or a specifically designed questionnaire.

PURPOSE

The purpose of this within-subject, crossover clinical trial was to investigate patient satisfaction levels in edentulous patients after rehabilitation with dentures fabricated using the NZ concept as compared with conventional dentures using a specific, question-oriented patient satisfaction questionnaire.

MATERIAL AND METHODS

The clinical trial included 52 participants. Each received one set of conventional dentures and another fabricated based on the NZ concept with a 1-month wash-out period. Participants randomly chose 1 of 2 closed opaque envelopes with 2 denture sequences, either conventional then NZ or NZ then conventional. Hence, participants were blinded to the dentures they wore. Patient satisfaction with each denture type was assessed 6 weeks after insertion by a blinded staff member using a 5-scale questionnaire developed for the most important functional aspects (esthetics, masticatory ability, retention, stability, speech, and comfort). The Wilcoxon Signed Rank test was used to compare the satisfaction scores of the 2 denture types (α=.05).

RESULTS

Patient satisfaction scores were significantly higher with the NZ dentures than with the conventional dentures in all aspects; P=.001 for question 2 (opinion of denture appearance) and P<.001 for all other questions.

CONCLUSIONS

NZ dentures offer significantly higher levels of patient satisfaction than conventional dentures in all functional aspects (retention, stability, masticatory ability, and speech) as well as in comfort and appearance.

Final-impression techniques and materials for making complete and removable partial dentures

BACKGROUND

Edentulism is relatively common and is often treated with the provision of complete or partial removable dentures. Clinicians make final impressions of complete dentures (CD) and removable partial dentures (RPD) using different techniques and materials. Applying the correct impression technique and material, based on an individual's oral condition, improves the quality of the prosthesis, which may improve quality of life.

OBJECTIVES

To assess the effects of different final-impression techniques and materials used to make complete dentures, for retention, stability, comfort, and quality of life in completely edentulous people.To assess the effects of different final-impression techniques and materials used to make removable partial dentures, for stability, comfort, overextension, and quality of life in partially edentulous people.

SEARCH METHODS

Cochrane Oral Health's Information Specialist searched the following databases: Cochrane Oral Health's Trials Register (to 22 November 2017), the Cochrane Central Register of Controlled Trials (CENTRAL) (Cochrane Register of Studies, to 22 November 2017), MEDLINE Ovid (1946 to 22 November 2017), and Embase Ovid (21 December 2015 to 22 November 2017). The US National Institutes of Health Trials Registry (ClinicalTrials.gov) and the World Health Organization International Clinical Trials Registry Platform were searched for ongoing trials. No restrictions were placed on language or publication status when searching the electronic databases, however the search of Embase was restricted by date due to the Cochrane Centralised Search Project to identify all clinical trials and add them to CENTRAL.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) comparing different final-impression techniques and materials for treating people with complete dentures (CD) and removable partial dentures (RPD). For CD, we included trials that compared different materials or different techniques or both. In RPD for tooth-supported conditions, we included trials comparing the same material and different techniques, or different materials and the same technique. In tooth- and tissue-supported RPD, we included trials comparing the same material and different dual-impression techniques, and different materials with different dual-impression techniques.

DATA COLLECTION AND ANALYSIS

Two review authors independently, and in duplicate, screened studies for eligibility, extracted data, and assessed the risk of bias for each included trial. We expressed results as risk ratios (RR) for dichotomous outcomes, and as mean differences (MD) or standardised mean differences (SMD) for continuous outcomes, with 95% confidence intervals (CI), using the random-effects model. We constructed 'Summary of findings' tables for the main comparisons and outcomes (participant-reported oral health-related quality of life, quality of the denture, and denture border adjustments).

MAIN RESULTS

We included nine studies in this review. Eight studies involved 485 participants with CD. We assessed six of the studies to be at high risk of bias, and two to be at low risk of bias. We judged one study on RPD with 72 randomised participants to be at high risk of bias.Overall, the quality of the evidence for each comparison and outcome was either low or very low, therefore, results should be interpreted with caution, as future research is likely to change the findings.Complete denturesTwo studies compared the same material and different techniques (one study contributed data to a secondary outcome only); two studies compared the same technique and different materials; and four studies compared different materials and techniques.One study (10 participants) evaluated two stage-two step, Biofunctional Prosthetic system (BPS) using additional silicone elastomer compared to conventional methods, and found no evidence of a clear difference for oral health-related quality of life, or quality of the dentures (denture satisfaction). The study reported that BPS required fewer adjustments. We assessed the quality of the evidence as very low.One study (27 participants) compared selective pressure final-impression technique using wax versus polysulfide elastomeric (rubber) material. The study did not measure quality of life or dentures, and found no evidence of a clear difference between interventions in the need for adjustments (RR 0.81, 95% CI 0.38 to 1.70). We assessed the quality of the evidence as very low.One study compared two stage-two step final impression with alginate versus silicone elastomer. Oral health-related quality of life measured by the OHIP-EDENT seemed to be better with silicone (MD 7.20, 95% CI 2.71 to 11.69; 144 participants). The study found no clear differences in participant-reported quality of the denture (comfort) after a two-week 'confirmation' period, but reported that silicone was better for stability and chewing efficiency. We assessed the quality of the evidence as low.Three studies compared single-stage impressions with alginate versus two stage-two step with elastomer (silicone, polysulfide, or polyether) impressions. There was no evidence of a clear difference in the OHIP-EDENT at one month (MD 0.05, 95% CI -2.37 to 2.47; two studies, 98 participants). There was no evidence of a clear difference in participant-rated general satisfaction with dentures at six months (MD 0.00, 95% CI -8.23 to 8.23; one study, 105 participants). We assessed the quality of the evidence as very low.One study compared single-stage alginate versus two stage-two step using zinc-oxide eugenol, and found no evidence of a clear difference in OHIP-EDENT (MD 0.50, 95% CI -2.67 to 3.67; 39 participants), or general satisfaction (RR 3.15, 95% CI 0.14 to 72.88; 39 participants) at six months. We assessed the quality of the evidence as very low.Removable partial denturesOne study randomised 72 participants and compared altered-cast technique versus one-piece cast technique. The study did not measure quality of life, but reported that most participants were satisfied with the dentures and there was no evidence of any clear difference between groups for general satisfaction at one-year follow-up (low-quality evidence). There was no evidence of a clear difference in number of intaglio adjustments at one year (RR 1.43, 95% CI 0.61 to 3.34) (very low-quality evidence).

AUTHORS' CONCLUSIONS

We conclude that there is no clear evidence that one technique or material has a substantial advantage over another for making complete dentures and removable partial dentures. Available evidence for the relative benefits of different denture fabrication techniques and final-impression materials is limited and is of low or very low quality. More high-quality RCTs are required.

Customized Cheek Plumper with Friction Lock Attachment for a Completely Edentulous Patient to Enhance Esthetics: A Clinical Report

Prosthetic rehabilitation of a completely edentulous patient should never be restricted to the replacement of missing teeth. The ultimate aim of complete denture treatment should be restoration of the full range of oral functions and esthetics. Slumped cheeks are always a concern for esthetically demanding complete denture patients. This article describes a simple, scientific, cost-effective technique to improve facial esthetics in a completely edentulous patient with the help of a cheek plumper. The technique used here implements the concept of neutral zone to precisely determine the amount of space available for the cheek plumper. The simple friction lock attachments that retained the cheek plumpers on the prosthesis were also fabricated after determining the space available in the appropriate areas. Thus an effort was made to keep the cheek plumpers unobtrusive yet effective to ensure complete integration of the prosthesis into the stomatognathic system.

Managing the Unstable Mandibular Complete Denture – Tooth Placement and the Polished Surface

Constructing satisfactory conventional mandibular complete dentures is often challenging in comparison to the upper counterpart partially due to differences in the anatomy of the denture-bearing area. This problem is exaggerated in the atrophic mandible, where supporting structures are frequently ill-defined and suboptimal in quality. Implant-retained prostheses offer well recognized benefits but are not always a feasible options, so conventional methods must be relied upon. The importance of impression quality and registration has been reviewed previously. This article aims to discuss the influence of tooth placement, the polished surfaces and the neutral zone on the success of lower dentures. Clinical relevance: This article highlights the importance that polished surface contouring and tooth prescription can have on the outcome of lower dentures. Techniques for assessing and recording the neutral zone are explained, along with alternative occlusal schemes.

Association of Neutral Zone Position with Age, Gender, and Period of Edentulism

PURPOSE

The changing dynamics of an aging mouth influence the position of the neutral zone (NZ). While the advantage of the NZ concept in complete denture treatment is quite established, what is not clearly understood is its position in relation to the crest of the residual ridge due to conflicting reports from previous studies. The purpose of this study was to investigate the distance and direction of NZ position in relation to crest of the residual ridge in edentulous patients and its association with age, gender, and period of edentulism.

MATERIALS AND METHODS

A cross-sectional study was conducted in 133 patients (70 males, 63 females) with a mean age of 58.81 ± 11.78 years. NZ recording was done using admix material by following standard procedures. Two metallic wires were adapted, one on the ridge and another on the center of the occlusal rims, and standardized digital radiographs were made. The position of NZ in relation to the crest of the residual ridge was recorded by noting the direction and measuring the distance between the adapted wires digitally at five locations (right molar, right premolar, incisor, left molar, left premolar regions).

RESULTS

Age, gender, and period of edentulism had no significant association with the position of NZ. No specific trend was observed in the in NZ position with a non-significant correlation.

CONCLUSIONS

Distance and the direction of neutral zone position in relation to crest of the residual ridge in edentulous patients bear no significant relationship with factors such as age, gender, and period of edentulism.

Effect of neutral zone technique on marginal bone loss around implant-supported overdentures

Aim:

The aim of this study was to compare changes in marginal bone height around immediately loaded implants supporting a mandibular overdenture constructed according to the neutral zone technique with changes around overdentures constructed according to the conventional methods.

Materials and Methods:

Twelve completely edentulous male patients were randomly allocated to two equal groups of patients. Patients in the first group received conventionally constructed complete dentures and patients in the second group received complete dentures constructed using the neutral zone record. All the patients received two single-piece titanium implants placed bilaterally in the mandibular canine regions using flapless surgery, which were then immediately loaded by the dentures. Marginal bone height was radiographically evaluated at baseline and 6, 12, and 18 months after implant loading.

Results:

There was a significant loss in marginal bone height around the supporting implants in each study group. However, no significant differences in marginal bone height were recorded between the study groups over the observation period (P > 0.05).

Conclusion:

Marginal bone height changes induced by overdentures constructed with neutral zone technique on immediately loaded implants are not different from those changes induced by overdentures constructed with a conventional method.

Presurgical implant-site assessment and restoratively driven digital planning

Cone-beam computed tomography imaging and 3-dimensional (3D) computer software allows for greatly enhanced visualization of bone, critical anatomy, and restorative plans. These systems allow clinicians to digitally process 3D images and restorative templates, facilitating dental implant planning. This article highlights the use of contemporary methods of digital assessment combined with traditional restorative philosophies to allow the clinician to plan implant positions based on "crown-down" clinical requirements. This approach permits clinicians to have more control over the implant treatment plan by creating ideal, virtual restorations and managing implant positions based on the virtual plan with simplified, cost-effective techniques.