Abstract The principles of occlusion have been researched and continuously developed over a period longer than 100 years. The focus is on teeth to teeth relationships – on the same arch and inter-arches – and the joint geometry. The occlusion is seen as the key for a functional integration of an aesthetic treatment and must be considered whenever anterior aesthetic restorations are to be placed. In the recent years, research has produced more data showing the impact of tooth wear on the modifications of the occlusal scheme and implicitly the influence on the aesthetic treatment long-term prognosis. Among these factors are airways patency, tongue size or head and body posture. This article shows two specific cases: in one Ryan’s case the occlusal scheme has been preserved while in Sabine’s case, the occlusal scheme has been altered. On both cases, the focus is on wear diagnostics in conjunction with muscles and joints homeostasis. Introduction Multiple aesthetic evaluations and design protocols (Digital Smile Design – DSD, Smile Designer Pro, Digital Smile 3D and others) have been introduced in the dental world and seem to become very popular in dentist acceptance and employment for patient treatment. The visualization benefits for the patient and the dentist are unequivocal. However, these systems are limited in assisting the dentist in functionally integrating the aesthetic proposals. In conjunction with such protocols, it is mandatory to be performed a thorough functional analysis that includes temporo-mandibular joints condition, head & neck muscles tonus, identification of occlusal scheme along with the structural integrity of biologic components (dental structures, periodontal, bone support, afferent proprioceptive receptors). The most recent research brings forth more data related to upper airway patency, the influence of blood oxygenation on the chemistry of on joint fluids, frequency and duration of parafunctions and the genetic as well as epigenetic influences on the development of pathology, compensation capacity and consequences to the aesthetic treatment success. The current diagnostic protocol proposed by Spear F. and associates takes in consideration Aesthetics, Function, Structural, and Biological Components (E.F.S.B.) while the treatment planning is established in the reverse order and executed to address all aspects simultaneously. While this process proves to be relatively comprehensive and elaborated, we believe there is a missing component: Timespan. The past and present is already addressed through anamnesis but data is often limited to the presence of pathology and not correlated with the individual physiology, especially developmental. The genetic determination, interaction with the environment and previous medical/dental procedures (which could fall under the category epigenetic influences) and challenge the compensatory mechanisms leading the patient close to the border of compensation range or into the pathology area (resulting in structural and functional degradation). Depending on the degree of treatment individualization to patient specific adaptability, challenges are compensated for a long period of time or not. The key question that needs answered is where within the compensation range is currently the patient and if the proposed treatment will:

  1. Further challenge the compensatory mechanisms but stay within the range of non -structural and -functional degradation.
  2. Further challenge the compensatory mechanisms and “push” them beyond the individual’s range of adaptation and lead to accelerated structural and functional degradation.
  3. Stabilize or improve (synergistic) the compensatory mechanisms so the patient will experience an increased range of adaptation in case of future health-related challenges.

Such quantification is difficult to establish and we hope that further studies will bring us closer to a distinct protocol of evaluating compensation capabilities. Nonetheless, clinicians experience nowadays a critical and somehow subjective evaluation of patient’s compensatory capabilities and adjust their treatments accordingly – ongoing differential diagnostics. Identifying the factors which led to the current developmental stage of the masticatory system and its respiratory, masticatory and phonetic characteristics can provide essential information in understanding the patient-specific biological compensatory mechanisms in relationship to the patient’s interaction with the environment. Sometimes, the quantification process of the above-mentioned factors cannot be performed while the patient is requesting rather fast aesthetic results. That is why we suggest a simple protocol consisting of the major questions, which instead of allowing in a comprehensive evaluation they rather establish functional and compensatory Risk. Answering “Yes” to any of these three questions prompts for more in-depth evaluation and possible delay of the aesthetic treatment.

  1. Is the present structural damage (missing tooth structure) a result of attrition (wear through tooth to tooth contact) or extraneous factors? It can happen that both conditions exists simultaneously, such in the cases of combined acidic erosion and bruxism. The damaged tooth structure could also occur due to trauma and this case we should ask if the tooth is the only structure impacted by functional and/structural degradation.
  2. Have compensatory tooth, periodontal, bony migrations occurred and if yes, do they have a stabilizing or detrimental structural/functional effect? Some of the most common examples are the accelerated attrition of mandibular anterior teeth with subsequent extrusion, abfractions, localized periodontal support failure, joints symptomatology and bony changes due to occlusal trauma.
  3. Are there any changes in the masticatory muscles tonus, mandibular condyles positions, upper airways patency or overall posture that lead to prolonged tooth-to-tooth contact (more than an average of 20 minutes a day) and/or excessive loading? A rather quick clinical and photographic analysis or wear facets, occlusal contacts pressure and timing can shed light into the amount of tooth structure loading and possible para-functions that can lead to a rapid aesthetic treatment failure.
Case #1 – Ryan Ryan is his early thirties, excellent health but unhappy with the appearance of his smile. Anamnesis and clinical examination does not bring forward any temporo-mandibular joints or masticatory muscle pathology. Airway patency in Centric Relation is adequate (no airway restrictions noted during forceful breathing). Stop-Bang questionnaire shows a low risk – 0 for Obstructive Sleep Apnea (OSA). Existing composite restoration in the anterior maxillary teeth are failing through marginal leakage and need to be replaced. The challenge is in establishing pleasing aesthetic proportions between left and right aspect of the maxillary dentition, in particular the width of#13 migrated in the place of 12 and the peg lateral #22. Before any aesthetic digital design is attempted, we asked the functional risk assessment questions:
Question 1 – Answer: Structural damage has probably occurred in the past and the current restorations are not failing due to occlusal trauma. Question 2 – Answer: Compensatory tooth migration have occurred to close the anodontia (or past extraction) of 12. The shortening of maxillary arch perimeter also led to a limitation of mandibular perimeter with consequent teeth incongruence in the anterior segment. Nevertheless, the bone support and periodontal health seem stable. Question 3 – Answer: Occlusal contacts distribution – static and dynamic – shows multiple posterior interferences during lateral and protrusive mandibular excursions.
The photographic wear analysis shows small wear facets on: incisal edge of 41, cuspid tip of 23, disto-lingual cusp of 17, disto-buccal cusp of 47. The facets’ edges are dull suggesting the past tense character of the attrition with absence of present occlusal overload. Corroborated data from the clinical exam, anamnezis and patient supervision over the period longer then 6 months leads to the conclusion that in spite of the un-equilibrated character of the occlusal relationships, the current functional setup is stable and is not leading to structural and functional degradation.
It is true that an orthodontic treatment for the mandibular arch might establish a better alignment of the anterior teeth (beneficial for the periodontal health of these teeth as well as promoting a better protrusive and lateral disclusive support) but this would require an increase in the dental arch perimeter, which in turn necessitates an increase of maxillary arch perimeter.
In this case though, the patient is maintaining an impeccable oral health and the periodontal disease risk is very low. In combination with a low occlusal risk, we then concluded that the aesthetic dilemma in anterior maxillary could be resolved only through limited treatment in the maxillary anterior teeth, without any further invasive treatment.
Only at this point in time we proceeded with an aesthetic digital smile design, a diagnostic wax-up and the fabrication of silicone prep guides. Once the case was finished, the occlusion scheme has not been altered and the patient was not provided with any occlusal protective splint. Based on the patient’s individual oral health risk assessment, we have established a six months prophylactic recall. Follow-up photography at 1 month, 6 months and 5 years show the structural and functional stability of the treatment confirming in spite of an unbalanced occlusal scheme (lack of cuspid disclusion, multiple posterior interferences in lateral excursion and the presence of high load spots during protrusion), the situation is stable and the choice of preserving patient’s occlusal setup was the right one.
Case #2 – Sabine
She is a healthy woman in her late forties, presenting with slightly elevated masticatory muscles tonus (sensitive to palpation – masseters bilateral 5 our 10, sternocleidomastoid at the mastoid insertion, bilateral out 10, anterior temporal, bilateral 3 out of 10), left TM joint capsular laxity (reciprocal clicking can be provoked through external auditory meatus finger pressure), TMJs – bilateral having full range of motion, absence of joint pain & crepitus and airways patency not limited in centric relation. The patient is complaining of “teeth braking down” and the structural analysis shows multiple teeth with failing restorations and repeated provisionalization. For this patient, the elevated masticatory muscles tonus and failing tooth structure integrity (Question 1 and 3 – Yes) raises the need of further evaluation. Photography wear analysis and T-Scan (Tekscan USA) bite analysis with the mandible tripod-ized in Centric Relation (Leaf Gauge, Dr. J. Long, 1973) shows posterior deflective interferences causing a protrusive slide of approximately 2-3 mm from the centric relation/first contact position to maximum intercuspation.
An analysis of the articulator-mounted casts – using a centric relation bite registration – replicates the deflective slide during clinical examination while allowing in identification of wear patterns consistent with the slide.
The wear facets margins are sharp suggesting the contemporary character of the para-function while the current structural degradation of the teeth correlated with the elevated muscle tonus strongly suggest a decompensated functional status. Left untreated, it will most likely lead to further pathology including tooth structure/periodontal failure with an aggravation of TM joint symptomatology. We also concluded that the amount tooth wear in the posterior segment is not matching patient’s chonorological age, strongly suggesting a pathological attritional activity.
We then decided that the patient’s occlusal scheme has to be altered through the elimination of the centric relation to centric occlusion premature contact and the deflective slide. The diagnostic wax-up exhibits cuspid and protrusive guidance with absent posterior interferences. The new occlusal scheme was first tested with an adjusted full coverage maxillary splint and the patient received very well the absence of the deflective contact. We progressively decreased the vertical dimension of occlusion (VDO) on the splint to get as close as possible to the treatment VDO. Upon the teeth preparation we fabricated a set of provisionals (AnaxCAD Temp, Anaxdent Germany) designed and milled following the diagnostic wax-up.
The patient again accepted the new occlusal setup very well, exhibiting normal muscle tonus and the absence of parafunctions.
The Stop-Bang questionnaire while wearing the provisionals shows an unmodified original low risk – 0 for Obstructive Sleep Apnea (OSA). Patient also received a wrist pulse-oximeter to wear over few nights and provide us with more reliable data regarding possible conflict between the new occlusal scheme and the airway patency.
The provisional uneventfully survived for more than a month, after which we proceeded with the seating of full-ceramic restorations. We equilibrated the occlusion using T-Scan (Tekscan USA) bite analysis and also recorded a video of the mandibular movements during protrusive and lateral excursions. The video together with the T-scan contact timing recording serves to identify the specific zones of resistance and pathway disturbances that could constitute a para-functional trigger.
In Sabine’s case, the change in the occlusal scheme was necessary and proved to be very beneficial for her, subjectively outlined also by the patient: “Beside a beautiful smile, I have no more headaches and neck muscle tension. I feel simply great!”
Conclusions: The answers to the functional questions can help establish the degree of functional/structural risk and identify the needs for more in-depth diagnostics prior to aesthetic treatments. We feel that by just answering the above questions, the predictability of aesthetic treatments can be greatly improved or even avoid invasive tooth substance removal through the employment of structurally minimally-invasive procedures such as orthodontic tooth movement for the purpose of optimized occlusal load distribution. Whenever possible, splint therapy and trial occlusal therapy with bonded composite materials can be invaluable steps in confirming the functional risk and the need for occlusal therapy before any wear-resistant ceramics are employed. On the same token, a greater predictability of patient compensatory capability for the treatment can be achieved.