Article
Oral health in the UK has improved over the past 30 years, as such, there has been a marked increase in the number of people retaining teeth and a steady decline in the prevalence of edentulous patients.1 The impact of this is that the routine fabrication of de novo complete dentures has reduced, thus, making it more difficult for general dental practitioners to gain the necessary experience to acquire this skill set. This problem is not confined to existing qualified dentists but is apparent in the undergraduate cohort. A reduction in the availability of edentulous cases for undergraduate teaching has been reported in the literature, which may be as low as two cases per student in some UK schools.2,3 While all of the stages involved in complete denture fabrication are equally important and can be read about in more detail in relevant textbooks, we focus on providing a method for practitioners who are inexperienced, or who infrequently fabricate complete dentures, to verify the aesthetic prescription of their maxillary occlusal rim before delivery to the technician.
The ‘jaw registration stage’ is often erroneously considered to be solely about recording the static intermaxillary relationship in centric relation. However, McCord and Grant4 highlighted the importance of creating and outlining the form of the upper denture during this visit to achieve an optimal aesthetic result. In clinical practice, dentists receive upper and lower wax rims, usually either on shellac or acrylic bases that are duly shaped into the desired form of the upper denture at the chairside. Wax is a suitable material for making record rims as it can be added to, subtracted from, and smoothed with a flame or hot instrument.5 Modification of the wax record rims is a simple way of creating the overall shapes that define the dentures' optimum forms. In complete denture construction, it is generally accepted that the maxillary incisal plane should be parallel to the interpupillary line. The occlusal plane should be set parallel to the ala-tragal line (Camper's line),4,5 as is commonly seen in the dentate patient. The exception to this would be if the patient had a cant in their previous natural dentition and wished for this to be incorporated into their maxillary complete denture.5
The Fox's occlusal plane guide or any device giving a horizontal plane reference, such as a wooden spatula, can be used to assess whether the occlusal rims are parallel to the interpupillary line and the ala-tragal line. In the authors' experience, judging whether the lines are parallel can be challenging for the inexperienced operator, or in situations where the patient cannot remain upright and still, owing to a movement disorder (eg Huntington's disease, Parkinson's syndrome, cerebral palsy).
The technique described below can alleviate the guesswork from this aspect of the jaw registration procedure and allow the occlusal rim to be modified before progressing to the denture construction's wax-trial stage.
Technique
Step 1: adjustment of the upper occlusal rim
Step 2: image capture
Any device with digital photograph capturing capabilities can be used to take a clinical photograph of the patient. The authors' preference is that clinical images are taken using a digital SLR camera with either a ring or twin flash. While it is not within the remit of this article to discuss detailed clinical photography, the following standard settings can be used to produce high quality, reproducible, portrait images:
Once the clinician feels that the aesthetic prescription of the upper occlusal rim is complete, a clinical photograph (Figure 1) is taken while standing directly in front of the patient with the Fox's bite plane and upper occlusal rim in situ. For this image, the clinician and dental assistant must ensure that the patient's head is not postured. To minimize this, the dental chair should be positioned upright, with the head in a neutral position facing forwards. The alatragal plane should be parallel to the floor. A second image should also be taken of the patient smiling without the Fox's bite plane in situ so that the markings of the centreline and canine lines can be seen (Figure 2).
Step 3: image upload
Once the image is taken, it is then transferred from the camera to a computer or tablet with Apple Keynote presentation software availability. (Apple Keynote is the author's preferred software application to modify and verify the aesthetic prescription, because it is intuitive and is easy to use for smile analysis. However, other similar software is available, such as Microsoft PowerPoint.)
Step 4: using the ‘grid reference tool’
The grid reference tool (Figure 3) available for download through the hyperlink or QR code at the end of this article can be used as a simple tool to overlay onto frontal facial portraits of patients providing a reference between the facial landmarks and the occlusal rim/Fox's bite plane. If there is an incisal cant present or the centreline or canine lines are judged to be incorrectly positioned, the wax rim can be adjusted before sending the occlusal rim to the technician. This will aid the clinician and the prosthetic laboratory technician with alignment and tooth positioning when constructing aesthetic complete dentures.
Step 5: overlaying the grid
Once the clinical photo is transferred into the presentation software, the grid reference tool is then overlaid on top to assess the alignment of the Fox's bite plane and occlusal rim with the facial landmarks. This can be achieved following the below steps:
Step 6: horizontal positioning adjustments
To ensure that the image matches the references, a subtle adjustment in the image position may be required. For example, rotation of the image may be required if the patient's head is tilted. The following adjustments (Figure 5) can be made on Apple Keynote once the image is clicked on:
Step 7: final verification
The last step is to ensure that all the facial references (inter-pupillary line and inner canthus of the eyes) are aligned with the grid correctly (Figure 4). Visual assessment is then made to see whether the Fox's bite plane is parallel to the horizontal grid lines. If this is the case, then the clinician can be confident that the incisal plane of the occlusal rim is parallel to the interpupillary line. If the Fox's bite plane is not parallel to the horizontal grid lines, then the clinician must carry out further adjustment to the wax and repeat the above process until the grid is parallel. Similarly, if in the smiling photo the canine lines are not coincident with a line from the inner canthi of the eyes to the alar of the nose, this can be adjusted before sending the occlusal rim to the technician (see Figure 6).
Step 8: transfer of final image to prosthetic laboratory technician
Once the clinician is satisfied, and the facial references are parallel with the corresponding references on the upper wax rim. Then the images with the grid overlayed on top can be captured and sent to the prosthetic laboratory technician to aid with constructing the denture wax try-in.
Conclusion
The above steps highlight how basic digital photo analysis can be used at the jaw registration stage in complete denture construction to verify the upper complete denture's aesthetic prescription. Ultimately, this tool serves to aid the clinician and the prosthetic laboratory technician when fabricating the maxillary complete denture, optimizing the final aesthetics.
To help clinicians and laboratory technicians with this process, the authors have compiled a free downloadable guide on how each step is undertaken. The presentation can be viewed and edited on a tablet or PC using Apple Keynote or Microsoft PowerPoint.
For online subscribers please follow the links below to download the free guide and grid reference tool.
QR code for Apple Keynote users:
QR code for Microsoft PowerPoint users:
Historical note on the cover image: Pig, boar and badger bristle, bonehandled toothbrushes
The first commercially available toothbrushes made in the UK were made by Addis in 1780. The bristles were made from pig bristles, boar or badger hair, and inserted into a cattle bone handle. Each toothbrush was handmade, with the bristles drawn into prepared graves in the bone handles or inserted by trepanning holes into the bone. Pig bristles were the cheapest, and the Siberian or Russian boar was considered superior due to stiffer bristles produced in the cold climate. However, the badger hair toothbrush was the most expensive, as the bristles were softer and thought to be less damaging to the teeth. The problem with a natural bristle toothbrush is that each bristle is a hollow filament, which harbours fluids and bacteria. The bristles could not be sterilized or put into hot water as the bristles soften and bend. In 1940, Addis launched the first nylon toothbrush called ‘Wisdom’. These toothbrushes were considered to be more hygienic, could be mass produced and were cheaper to buy, heralding the era of the modern toothbrush.