Occlusal contacts and tooth wear

Masticatory Adaptation to Occlusal Changes

This review deals with the frequent wide variability of masticatory capacity/incapacity. Neither researchers nor clinicians have taken sufficient account of this variability despite its implications for nutrition. Mastication in normal healthy oral conditions is first described, followed by a short presentation of the mechanisms of masticatory adaptation in the nervous system. Capacity, incapacity, and successful compensatory adaptation of mastication are then defined, along with the different methods used for their evaluation. Examples of adaptation needs are given, such as those concomitant with dental wear or occlusal changes. Finally, given its vital importance for deeply impaired mastication/deglutition function, the impact of masticatory adaptation processes on nutrition is examined.

Antagonist enamel wear of tooth-supported monolithic zirconia posterior crowns in vivo: A systematic review

STATEMENT OF PROBLEM

An assessment of the evidence for the antagonist enamel wear of tooth-supported monolithic zirconia posterior crowns is lacking.

PURPOSE

The purpose of this systematic review was to identify and summarize clinical studies related to the antagonist enamel wear of tooth-supported monolithic zirconia posterior crowns.

MATERIAL AND METHODS

PubMed, Embase, and Cochrane library searches were performed and complemented by manual searches from database inception to December 25, 2017, for title and abstract analysis.

RESULTS

Initially, 198 articles were obtained through database searches. Twenty-one articles were selected for full-text analysis, and 5 studies met the inclusion criteria. Because of the heterogeneity in design, surface treatment, measurement methods, and wear parameters, a meta-analysis was not possible. The selected studies were analyzed regarding the antagonist natural enamel wear of zirconia, measurement methods, and surface treatment. The results of the antagonist enamel wear varied widely, which made comparing them scientifically with absolute values difficult.

CONCLUSIONS

This review indicated that the antagonist enamel wear of zirconia was similar to or more than that of natural teeth but less than that of metal-ceramics. Additional properly designed, longer follow-up clinical trials with larger sample sizes are needed to evaluate the antagonist enamel wear of monolithic zirconia crowns in vivo.

Methods for quantitative measurement of tooth wear using the area and volume of virtual model cusps

Purpose

Clinicians must examine tooth wear to make a proper diagnosis. However, qualitative methods of measuring tooth wear have many disadvantages. Therefore, this study aimed to develop and evaluate quantitative parameters using the cusp area and volume of virtual dental models.

Methods

The subjects of this study were the same virtual models that were used in our former study. The same age group classification and new tooth wear index (NTWI) scoring system were also reused. A virtual occlusal plane was generated with the highest cusp points and lowered vertically from 0.2 to 0.8 mm to create offset planes. The area and volume of each cusp was then measured and added together. In addition to the former analysis, the differential features of each cusp were analyzed.

Results

The scores of the new parameters differentiated the age and NTWI groups better than those analyzed in the former study. The Spearman ρ coefficients between the total area and the area of each cusp also showed higher scores at the levels of 0.6 mm (0.6A) and 0.8A. The mesiolingual cusp (MLC) showed a statistically significant difference (P<0.01) from the other cusps in the paired t-test. Additionally, the MLC exhibited the highest percentage of change at 0.6A in some age and NTWI groups. Regarding the age groups, the MLC showed the highest score in groups 1 and 2. For the NTWI groups, the MLC was not significantly different in groups 3 and 4. These results support the proposal that the lingual cusp exhibits rapid wear because it serves as a functional cusp.

Conclusions

Although this study has limitations due to its cross-sectional nature, it suggests better quantitative parameters and analytical tools for the characteristics of cusp wear.

Evaluation of the effectiveness of the new tooth wear measurement parameters

Nowadays, there has been an increasing interest in the preservation of natural dentition and the proper occlusion related to tooth wear for quality of life. To overcome the problems of the existing qualitative tooth wear analysis method, virtual three-dimensional models have been used. This study was designed to develop and validate a new quantitative method using tooth wear measurement parameters with angles obtained from virtual vectors and planes of the three-dimensional models. Sixteen parameters were evaluated in the virtual models of 20 students (7.57±1.55 years old) and 20 adults (56.85±6.34 years old). There were 12 angle and 4 height parameters, and the number of parameters measured from the virtual planes and vectors were 10 and 6, respectively. For each parameter, means and standard deviations were calculated, and an unpaired sample t test was performed to compare the young and the adult groups. Also, differences between the means were determined and expressed as percentages. The results were statistically significant between the two groups (P<0.001). In general, parameters using virtual vectors showed greater change than virtual plane. Although there were statistically significant differences among all parameters using virtual planes (P<0.001), the changes of the three angles were similar, except distolingual cusp angle. It was found that the parameters using virtual vectors were effective and tooth wear took place in both buccal and lingual cusps. Likewise, the validation of the new measurement parameters suggests that they can also be applied in the assessment of tooth wear related to dental biomaterials.

Estimation of the reliability of all-ceramic crowns using finite element models and the stress-strength interference theory

The reliability of all-ceramic crowns is of concern to both patients and doctors. This study introduces a new methodology for quantifying the reliability of all-ceramic crowns based on the stress-strength interference theory and finite element models. The variables selected for the reliability analysis include the magnitude of the occlusal contact area, the occlusal load and the residual thermal stress. The calculated reliabilities of crowns under different loading conditions showed that too small occlusal contact areas or too great a difference of the thermal coefficient between veneer and core layer led to high failure possibilities. There results were consistent with many previous reports. Therefore, the methodology is shown to be a valuable method for analyzing the reliabilities of the restorations in the complicated oral environment.

Inter-disciplinary management of a patient with severely attrited teeth

With increased awareness about dental esthetics, multidisciplinary periodontal therapy has begun to gain momentum. Management of severely attrited teeth is a challenging situation and is dealt with a multidisciplinary approach. In cases of severe tooth wear, the crown height is drastically reduced, in some cases up to the gingival level. This might require a contribution from the disciplines of endodontics, periodontics, orthodontics and prosthodontics for predictable results. Herein we describe the management of one such case.

The evolution of tooth wear indices

Tooth wear--attrition, erosion and abrasion-is perceived internationally as an ever-increasing problem. Clinical and epidemiological studies, however, are difficult to interpret and compare due to differences in terminology and the large number of indices that have been developed for diagnosing, grading and monitoring dental hard tissue loss. These indices have been designed to identify increasing severity and are usually numerical. Some record lesions on an aetiological basis (e.g. erosion indices), others record lesions irrespective of aetiology (tooth wear indices); none have universal acceptance, complicating the evaluation of the true increase in prevalence reported. This article considers the ideal requirements for an erosion index. It reviews the literature to consider how current indices have evolved and discusses if these indices meet the clinical and research needs of the dental profession.

Squamous cell carcinoma of the oral cavity: a case series analysis of clinical presentation and histological grading of 1,425 cases from Iraq

Peoples in Iraq face a mixture of health hazards associated with poverty. Oral cancer is a major public health issue worldwide; it remains a highly lethal and disfiguring disease. It is primarily a disease of epithelial origin. A total of 1,425 cases of histologically diagnosed squamous cell carcinoma collected from the main centers of pathology in Iraq were analyzed according to age, sex, site, patient complaints at the time of presentation, and histological grading. Patients at their fifth decade of life were the most commonly affected with a male-to-female ratio of 2:1. The lower lip was the most commonly affected site followed by the tongue. The most common clinical complain was ulceration and swelling. More than 70% of the cases were well-differentiated squamous cell carcinoma. Oral cancer is increasingly seen as a major health problem-In line with general trend in the region, the need for interprofessional health care delivery approaches for reducing oral cancer mortality and improving patient's quality of life.

The lateral leeway in the habitual intercuspation: experimental studies and literature review

The habitual intercuspation is used ubiquitous for manufacturing small dental restorations. However, a little is known on its precision. The aim of the present study was therefore to investigate the unambiguity and accuracy of the habitual occlusion in mounted plaster casts from fully dentate persons. Eighty-one fully dentate volunteers, 36 women and 45 men aged 26.8 +/- 6.2 years (18-55 years), with minor fillings and no signs or symptoms of TMD took part in the experiments. Silicone impressions were taken, poured with stone plaster and the obtained casts mounted into Dentatus ARL(R)- articulators using an individual face bow transfer. Subsequently, the models were transferred to a custom-made measuring articulator where the lateral leeway and the accuracy of the hand-held habitual intercuspation were quantified in the condylar area. Measurements were repeated seven times with the upper cast pushed either to the maximum right or the maximum left intercuspation. The hand-held habitual intercuspation of upper and lower cast proved ambiguous in 57% of pairs of casts. The average lateral leeway of the habitual intercuspation in the condylar area was 0.10 +/- 0.05 mm (0-0.51 mm; median 0.07 mm) between the maximum right and left occlusal positions. The average accuracy of three repeated measurements was 0.22 +/- 0.09 mm (0.02-1.17 mm; median 0.16 mm). Natural occlusal surfaces in a full dentition do not guarantee an unambiguous habitual intercuspation of the plaster casts. The described leeway and technical limits might be possible causes for occlusal adjustments that are sometimes necessary when inserting restorations manufactured in habitual intercuspation.

Age and gender-related differences in premolar and molar functional areas

The aim of the present study was to underline the difference in premolar-molar functional areas according to both age and gender in a human adult population. Premolar and molar series were marked manually on opposed casts with articulating paper and functional areas were evaluated by quantification of these markings. It was noticed that on average larger functional areas were displayed by the older group (19 individuals, mean age 71.2 years, minimum 68 years, maximum 73 years) in comparison with the younger one (24 individuals, mean age 27.4 years, minimum 22 years; maximum 33 years). It was also observed that the average total functional area (4 hemiarches) was larger in the male subgroup (n: 23; mean age 45; young adults, 14; old adults, 9) compared with the female one (n: 20; mean age 49; young adults, 10; old adults, 10). Nevertheless, this gender difference in premolar-molar functional areas was related to the individual occlusal areas. As a matter of fact, when the individual occlusal area was taken into account for each series in the form of a ratio (functional area/occlusal area), the values obtained were not different between both gender subgroups studied. When comparing premolar and molar functional ratios (functional area/occlusal area) between age groups, it appears that the values obtained were slightly higher for the premolar series (ratios for young and older adults, respectively: Premolar series: 23.6+/-7.5%, 30+/-6.5%; Molar series: 23.1+/-6.8%, 27.3+/-6.7%). This difference was interpreted in relation to the reference (occlusal area) chosen.

A mathematical model of mandibular movement on the Hanau articulator and computerized simulation system of dynamic occlusion for complete denture

This study is concerned with the construction of a mathematical model of mandibular movement on the Hanau articulator and a complete denture occlusion simulation system (CDOSS) in the field of dental restoration. On the basis of the theory of spatial mechanisms, degrees of freedom in the kinematic chain of the Hanau articulator are analysed, and a hypothesis of constraints is presented to obtain constrained motion. Then, a series of mathematical expressions are derived to describe the three dimensional mandibular movement on the Hanau articulator. By adopting techniques and tools such as laser scanning, computer graphics, and computer databases, a 3D digitized model of complete denture is reconstructed, and a CDOSS is developed. With the aid of this software, the visualization and diagnosis of mandibular movement can be easily realized. One edentulous case discussed in this study shows that CDOSS provides a useful tool to deal with the functional aspects of occlusal morphology in a diagnostic and therapeutic sense.

Tooth wear in maxillary anterior teeth from 14 to 23 years of age

Using a planimetric method, the size of horizontal wear facets on maxillary anterior teeth was studied longitudinally in the permanent dentition of 35 subjects at ages 14, 18, and 23?years. The study subjects had not previously undergone any orthodontic treatment and had Class I occlusion. We studied the association between the amount of wear and reported parafunctions and maximal bite force. Total wear areas in age groups 14, 18, and 23 years were 29.5 mm2 (SD 11.4), 39.1 mm2 (SD 12.7), and 45.0 mm2 (SD 13.0), respectively. The total wear area increased significantly both from 14 to 18 years of age and from 18 to 23 years of age (p <0.0001). Between 18 and 23?years of age, the maxillary canines showed strongest wear, although the central incisors had largest wear facets. It can be concluded that wear of permanent anterior teeth is a continuous phenomenon in adolescence and young adulthood.

The development of a new index for measurement of incisal/occlusal tooth wear

A number of indices have been developed for the measurement of tooth surface loss but they have not achieved universal acceptance. The aim of this study was to develop a new index suitable for the monitoring of incisal/occlusal tooth wear on serial study models. The new index recorded incisal/cuspal wear for individual teeth. Each tooth was scored on a six-point scale ranging from 0-5. Six assessors evaluated the index and it was applied to baseline and sequential models taken after 20 years. The study demonstrated the value of maintaining long-term dental records in the form of study models for monitoring progressive tooth wear.

Correlations between functional and occlusal tooth-surface areas and food texture during natural chewing sequences in humans

The dental-arch surfaces preferentially used in mastication were studied by measuring functional and occlusal surface areas and comparing these to the number of chews required to swallow foods of different texture properties. The functional surface of the teeth was defined as the total area of visible wear facets on post-incisal teeth, adding to it the contacting areas of restored teeth where no facets were visible. Occlusal surface area was taken as the total area of the occluding parts of post-incisal teeth. Both surfaces were measured with computer image processing on dental-stone casts of the teeth of 31 young adults. Functional surface areas (mean 168 mm(2), four quadrants) were positively correlated with occlusal surface areas (mean 739 mm(2), four quadrants). The left:right area ratios were more variable for functional than for occlusal surfaces. Functional surface-area ratios markedly different from 1.0 might reflect functional side-preponderance of masticatory activity. Correlations between tooth surface area and the number of cycles were examined with five different food samples of known texture during side-imposed mastication. Depending on the elastic moduli of the foods, significant negative correlations were found between the left:right ratios of functional or occlusal surface areas and the left:right ratios of cycle numbers. The rheological properties of the food particles chewed were assumed to be the key factor in the correlations with either the functional or anatomical occlusal surfaces.

Anthropology, tooth wear, and occlusion ab origine

The purpose of this essay is to emphasize that anthropology, the study of man in his environments, is a potent tool for scientific discovery and inspiration in dental science. It attempts to capture flashes of creative anthropological insight which have illuminated studies of tooth wear and occlusion in the past. While it documents contributions, understandings, and misunderstandings from Australian and New Zealand dentists, it is not a hagiography. The real saint of this essay is the Australian aborigine. For when men and women are understood in their environments, much is learned from them which challenges preconceptions of our dental science culture. The essay concludes that new, contemporary Australian culture needs to be studied by anthropological approaches if we are to understand how dental erosion is exacerbating tooth wear and damaging the occlusions of contemporary Australians. Much remains to be discovered about contemporary lifestyles, habits, and diets that lead to dental erosion, the principal cause of contemporary tooth wear in this part of the world.

Dental erosion and bruxism. A tooth wear analysis from south east Queensland

Tooth-tissue loss from erosion and attrition from bruxism were associated findings in 104 patients with excessive toothwear from South East Queensland. Approximately one-third of these subjects had been given a diagnosis of bruxism prior to referral. After a structured interview and clinical examination, the prevailing diagnosis was tooth erosion associated with occupational or sports-related dehydration, and one-third of the subjects were provisionally classified as bruxers. Eight items of clinical history and examination, designed to differentiate bruxers from non-bruxers, were analysed retrospectively from their records. These clinical items, by which the diagnosis of bruxism might be made, segregated the subjects into three groups of equal size, 'bruxers, possible bruxers and non-bruxers,' by a notional score for bruxism. The presence of occlusal attrition or erosion on the sextants of the dentitions was determined by scanning electron microscopic criteria on epoxy resin dental casts. The incidence of attrition versus erosion was compared between the three groups. The hypothesis was that attrition would be found on more sextants of bruxers than non-bruxers. Erosion predominated in virtually all sextants in all three groups, to the virtual exclusion of attrition in the molar sextants. The exception was the mandibular anterior sextant, where more sextants in bruxers were affected by attrition. Thus extrinsic or intrinsic acid erosion was strongly associated with occlusal tooth wear found in bruxers. Conversely, tooth-wear patterns were unreliable indicators of a bruxing habit, for attrition alone was often found on acid-exposed teeth. Thus, even if a patient is suspected of having bruxism, dental erosion is more likely the cause of tooth-tissue loss than attrition, especially in the dehydrating environment of South East Queensland.

Three-year follow-up of five posterior composites: SEM study of differential wear

Assessing the wear of both enamel and composite at a shared occlusal contact area offers the opportunity to determine the differential wear between enamel and composite on the same tooth. Differential wear measurements were carried out on five posterior composite materials with an accurate 3D-measuring technique. The distinct wear step between enamel and composite was visualized by means of scanning electron photomicrographs. Both investigated ultrafine midway-filled and fine compact-filled composites (Willems et al., 1992a) have a considerably higher differential wear value and are, therefore, less suitable for rehabilitation of posterior teeth than are the ultrafine compact-filled composites, which have, in this study, a very satisfactory differential wear rate and appear to be highly wear resistant materials suitable for use in stress-bearing areas.

Occlusal contact area and temporomandibular joint symptoms

A new method for quantitative occlusal measurement is presented. In this study occlusal contact areas in 79 patients with or without temporomandibular joint symptoms were assessed from the simple wax bite. The area of occlusion has showed no distinct differences between the two groups. The occlusal contacts did not show any significant correlations with temporomandibular joint dysfunctions.

Supraeruption of the unopposed maxillary first molar

Supraeruption of the maxillary first molar in the absence of the mandibular first molar was observed in subjects with both normal and pathologic periodontics. Both the migration of the gingival margin and the increase in the crown height were evaluated in terms of the length of time the antagonist tooth had been missing. Values obtained were compared with those of a reference group with complete normal dentitions. The results show that in the first years following the loss of the opposing tooth, supraeruption is mainly due to growth of the periodontium. Later or in the case of periodontal pathosis, tooth movement beyond the occlusal plane is due principally to active eruption.

A study of human jaw movements deduced from scratches on occlusal wear facets

In a previous investigation, scratches on tooth wear facets provided information about functional movements of the mandible in the occlusal range. Depending on the type of facet observed, two or three main directions were found. The aim now was to answer two questions: (1) how long does it take for a newly formed scratch to disappear? and (2) do the observed orientations of the scratches change over a long period of time? Eleven wear facets from lower first molars were analysed in four subjects with good natural dentition. Scratches recorded on cellulose replicas were observed under an interference microscope. The same wear facets were recorded one, two, three and six months later. From the photographs of the replicas, a sample of scratches was selected at random and their direction was measured. In the first part of the study, scratches absent at the time of the first observation appeared one month later; 87% of the new scratches had disappeared after one month. Ninety-six percent of the same group of scratches had disappeared after two months. In the second part of the study the angle made by each scratch with the sagittal plane was recorded. It was found that: (1) jaw movements in their occlusal phase can take any possible direction and (2) the distribution of the observed scratches was not random; preferential orientations exist and those present on the working facets are different from those on the non-working facets. Similar orientations were identified 6 months later.

Development of horizontal tooth wear in maxillary anterior teeth from five to 18 years of age

Sizes of horizontal wear facets of maxillary anterior teeth were studied longitudinally from the primary dentition at age five to the young adult dentition at the age of 18 years. By a planimetric method, we calculated the wear areas on dental casts taken at the ages of five, ten, 14, and 18 years from the dentition of 39 healthy, orthodontically untreated subjects with good morphological occlusion. For young adults, we also studied the association between the amount of wear and reported parafunctions, maximal bite force, salivary buffer capacity, salivary flow rate, and some cephalometric variables. Size of wear facets on all anterior teeth increased with age. Significant correlations were found between the total wear areas of the six anterior primary teeth at five years of age and those of their permanent successors at age 14 (r = 0.44) and 18 (r = 0.39). For an individual, tooth wear at five years of age was, however, of low predictive value for tooth wear in young adulthood, whereas tooth wear at 14 years of age predicted it well (r = 0.89). Highest correlations between tooth wear and background factors at 18 years of age were found for maximal anterior bite force (r = 0.44) and for the size of the gonial angle (r = -0.31). Wear of anterior teeth was not associated with reported parafunctions in young adulthood.

Number and location of occlusal contacts in intercuspal position

Records of intercuspal position were made in 45 healthy young adults with morphologically normal occlusions. The observed perforations were analyzed according to the frequency of occlusal contacts. Most subjects had asymmetric distribution in number and location of occlusal contacts. Regardless of symmetry, a significantly higher number of subjects had approximately seven contacts on each side that were located between all posterior teeth. Contacts were most frequent between maxillary and mandibular first and second molars.

Effect of bilateral asymmetric tooth clenching on load distribution at the mandibular condyles

The effects of balancing-side tooth contacts on temporomandibular joint loads are unclear. We used a 3-D computer model to calculate the magnitude and direction of temporomandibular reaction forces during simulated clenching on interocclusal acrylic resin shims and between natural teeth. Muscle tensions were proportioned according to the task modeled. Working-side tooth contacts included the canine alone, as well as group function, and occlusal loads were progressively shifted toward a posterior contralateral simple balancing contact. In the acrylic resin shim experiments, group function with simple balancing contact yielded the highest forces at the load point and at both temporomandibular joints. Movement of the occlusal load toward the balancing side produced greater, anteriorly oriented forces on the working condyle. For natural teeth, changes in the angle of resultant tooth force (simulating facet angulation) greatly influenced condylar forces. As the occlusal load moved toward the balancing side, greater and more laterally oriented forces were produced on the balancing condyle. Unilateral clenching on the canine produced the least condylar and bite forces. The simulation involving natural teeth offers a possible explanation for deviations in form and osteoarthrosis at the temporomandibular joints.

Quantitative in vivo wear of human enamel

In this study, the attrition wear, also called occlusal-contact-area wear, of human enamel was measured quantitatively with a computerized three-dimensional measuring technique over a period of four years. Tooth replicas from a clinical trial were used. A running-in wear period after restorative treatment, followed by steady-state wear, was suggested. The average steady-wear rate on occlusal contact areas was about 29 microns per year for molars and about 15 microns per year for premolars.